:sparkles: Implement Page bundling and image handling

This commit is not the smallest in Hugo's history.

Some hightlights include:

* Page bundles (for complete articles, keeping images and content together etc.).
* Bundled images can be processed in as many versions/sizes as you need with the three methods `Resize`, `Fill` and `Fit`.
* Processed images are cached inside `resources/_gen/images` (default) in your project.
* Symbolic links (both files and dirs) are now allowed anywhere inside /content
* A new table based build summary
* The "Total in nn ms" now reports the total including the handling of the files inside /static. So if it now reports more than you're used to, it is just **more real** and probably faster than before (see below).

A site building  benchmark run compared to `v0.31.1` shows that this should be slightly faster and use less memory:

```bash
▶ ./benchSite.sh "TOML,num_langs=.*,num_root_sections=5,num_pages=(500|1000),tags_per_page=5,shortcodes,render"

benchmark                                                                                                         old ns/op     new ns/op     delta
BenchmarkSiteBuilding/TOML,num_langs=1,num_root_sections=5,num_pages=500,tags_per_page=5,shortcodes,render-4      101785785     78067944      -23.30%
BenchmarkSiteBuilding/TOML,num_langs=1,num_root_sections=5,num_pages=1000,tags_per_page=5,shortcodes,render-4     185481057     149159919     -19.58%
BenchmarkSiteBuilding/TOML,num_langs=3,num_root_sections=5,num_pages=500,tags_per_page=5,shortcodes,render-4      103149918     85679409      -16.94%
BenchmarkSiteBuilding/TOML,num_langs=3,num_root_sections=5,num_pages=1000,tags_per_page=5,shortcodes,render-4     203515478     169208775     -16.86%

benchmark                                                                                                         old allocs     new allocs     delta
BenchmarkSiteBuilding/TOML,num_langs=1,num_root_sections=5,num_pages=500,tags_per_page=5,shortcodes,render-4      532464         391539         -26.47%
BenchmarkSiteBuilding/TOML,num_langs=1,num_root_sections=5,num_pages=1000,tags_per_page=5,shortcodes,render-4     1056549        772702         -26.87%
BenchmarkSiteBuilding/TOML,num_langs=3,num_root_sections=5,num_pages=500,tags_per_page=5,shortcodes,render-4      555974         406630         -26.86%
BenchmarkSiteBuilding/TOML,num_langs=3,num_root_sections=5,num_pages=1000,tags_per_page=5,shortcodes,render-4     1086545        789922         -27.30%

benchmark                                                                                                         old bytes     new bytes     delta
BenchmarkSiteBuilding/TOML,num_langs=1,num_root_sections=5,num_pages=500,tags_per_page=5,shortcodes,render-4      53243246      43598155      -18.12%
BenchmarkSiteBuilding/TOML,num_langs=1,num_root_sections=5,num_pages=1000,tags_per_page=5,shortcodes,render-4     105811617     86087116      -18.64%
BenchmarkSiteBuilding/TOML,num_langs=3,num_root_sections=5,num_pages=500,tags_per_page=5,shortcodes,render-4      54558852      44545097      -18.35%
BenchmarkSiteBuilding/TOML,num_langs=3,num_root_sections=5,num_pages=1000,tags_per_page=5,shortcodes,render-4     106903858     86978413      -18.64%
```

Fixes #3651
Closes #3158
Fixes #1014
Closes #2021
Fixes #1240
Updates #3757

43 files changed, 3206 insertions, 2006 deletions

diff --git a/hugolib/alias.go b/hugolib/alias.go
index a3fe5c24a..dbb864384 100644
--- a/hugolib/alias.go
+++ b/hugolib/alias.go
@@ -109,7 +109,7 @@ func (s *Site) publishDestAlias(allowRoot bool, path, permalink string, p *Page)
 		return err
 	}
 
-	return s.publish(targetPath, aliasContent)
+	return s.publish(&s.PathSpec.ProcessingStats.Aliases, targetPath, aliasContent)
 
 }
 
diff --git a/hugolib/alias_test.go b/hugolib/alias_test.go
index 1d6824dba..abbda5f35 100644
--- a/hugolib/alias_test.go
+++ b/hugolib/alias_test.go
@@ -51,7 +51,9 @@ func TestAlias(t *testing.T) {
 	writeSource(t, fs, filepath.Join("content", "page.md"), pageWithAlias)
 	writeSource(t, fs, filepath.Join("layouts", "_default", "single.html"), basicTemplate)
 
-	buildSingleSite(t, deps.DepsCfg{Fs: fs, Cfg: cfg}, BuildCfg{})
+	s := buildSingleSite(t, deps.DepsCfg{Fs: fs, Cfg: cfg}, BuildCfg{})
+
+	require.Len(t, s.rawAllPages, 1)
 
 	// the real page
 	th.assertFileContent(filepath.Join("public", "page", "index.html"), "For some moments the old man")
diff --git a/hugolib/config.go b/hugolib/config.go
index 62098aeea..c83f38cce 100644
--- a/hugolib/config.go
+++ b/hugolib/config.go
@@ -64,22 +64,21 @@ func LoadConfig(fs afero.Fs, relativeSourcePath, configFilename string) (*viper.
 
 	v.RegisterAlias("indexes", "taxonomies")
 
-	// Remove these in Hugo 0.23.
+	// Remove these in Hugo 0.33.
 	if v.IsSet("disable404") {
-		helpers.Deprecated("site config", "disable404", "Use disableKinds=[\"404\"]", false)
+		helpers.Deprecated("site config", "disable404", "Use disableKinds=[\"404\"]", true)
 	}
 
 	if v.IsSet("disableRSS") {
-		helpers.Deprecated("site config", "disableRSS", "Use disableKinds=[\"RSS\"]", false)
+		helpers.Deprecated("site config", "disableRSS", "Use disableKinds=[\"RSS\"]", true)
 	}
 
 	if v.IsSet("disableSitemap") {
-		// NOTE: Do not remove this until Hugo 0.24, ERROR in 0.23.
-		helpers.Deprecated("site config", "disableSitemap", "Use disableKinds= [\"sitemap\"]", false)
+		helpers.Deprecated("site config", "disableSitemap", "Use disableKinds= [\"sitemap\"]", true)
 	}
 
 	if v.IsSet("disableRobotsTXT") {
-		helpers.Deprecated("site config", "disableRobotsTXT", "Use disableKinds= [\"robotsTXT\"]", false)
+		helpers.Deprecated("site config", "disableRobotsTXT", "Use disableKinds= [\"robotsTXT\"]", true)
 	}
 
 	if err := loadDefaultSettingsFor(v); err != nil {
@@ -176,6 +175,7 @@ func loadDefaultSettingsFor(v *viper.Viper) error {
 	v.SetDefault("contentDir", "content")
 	v.SetDefault("layoutDir", "layouts")
 	v.SetDefault("staticDir", "static")
+	v.SetDefault("resourceDir", "resources")
 	v.SetDefault("archetypeDir", "archetypes")
 	v.SetDefault("publishDir", "public")
 	v.SetDefault("dataDir", "data")
diff --git a/hugolib/datafiles_test.go b/hugolib/datafiles_test.go
index b62fb197d..cdc5e0684 100644
--- a/hugolib/datafiles_test.go
+++ b/hugolib/datafiles_test.go
@@ -27,16 +27,15 @@ import (
 	jww "github.com/spf13/jwalterweatherman"
 
 	"github.com/gohugoio/hugo/parser"
-	"github.com/gohugoio/hugo/source"
 	"github.com/stretchr/testify/require"
 )
 
 func TestDataDirJSON(t *testing.T) {
 	t.Parallel()
 
-	sources := []source.ByteSource{
-		{Name: filepath.FromSlash("data/test/foo.json"), Content: []byte(`{ "bar": "foofoo"  }`)},
-		{Name: filepath.FromSlash("data/test.json"), Content: []byte(`{ "hello": [ { "world": "foo" } ] }`)},
+	sources := [][2]string{
+		{filepath.FromSlash("data/test/foo.json"), `{ "bar": "foofoo"  }`},
+		{filepath.FromSlash("data/test.json"), `{ "hello": [ { "world": "foo" } ] }`},
 	}
 
 	expected, err := parser.HandleJSONMetaData([]byte(`{ "test": { "hello": [{ "world": "foo"  }] , "foo": { "bar":"foofoo" } } }`))
@@ -51,8 +50,8 @@ func TestDataDirJSON(t *testing.T) {
 func TestDataDirToml(t *testing.T) {
 	t.Parallel()
 
-	sources := []source.ByteSource{
-		{Name: filepath.FromSlash("data/test/kung.toml"), Content: []byte("[foo]\nbar = 1")},
+	sources := [][2]string{
+		{"data/test/kung.toml", "[foo]\nbar = 1"},
 	}
 
 	expected, err := parser.HandleTOMLMetaData([]byte("[test]\n[test.kung]\n[test.kung.foo]\nbar = 1"))
@@ -67,12 +66,12 @@ func TestDataDirToml(t *testing.T) {
 func TestDataDirYAMLWithOverridenValue(t *testing.T) {
 	t.Parallel()
 
-	sources := []source.ByteSource{
+	sources := [][2]string{
 		// filepath.Walk walks the files in lexical order, '/' comes before '.'. Simulate this:
-		{Name: filepath.FromSlash("data/a.yaml"), Content: []byte("a: 1")},
-		{Name: filepath.FromSlash("data/test/v1.yaml"), Content: []byte("v1-2: 2")},
-		{Name: filepath.FromSlash("data/test/v2.yaml"), Content: []byte("v2:\n- 2\n- 3")},
-		{Name: filepath.FromSlash("data/test.yaml"), Content: []byte("v1: 1")},
+		{filepath.FromSlash("data/a.yaml"), "a: 1"},
+		{filepath.FromSlash("data/test/v1.yaml"), "v1-2: 2"},
+		{filepath.FromSlash("data/test/v2.yaml"), "v2:\n- 2\n- 3"},
+		{filepath.FromSlash("data/test.yaml"), "v1: 1"},
 	}
 
 	expected := map[string]interface{}{"a": map[string]interface{}{"a": 1},
@@ -85,10 +84,10 @@ func TestDataDirYAMLWithOverridenValue(t *testing.T) {
 func TestDataDirMultipleSources(t *testing.T) {
 	t.Parallel()
 
-	sources := []source.ByteSource{
-		{Name: filepath.FromSlash("data/test/first.toml"), Content: []byte("bar = 1")},
-		{Name: filepath.FromSlash("themes/mytheme/data/test/first.toml"), Content: []byte("bar = 2")},
-		{Name: filepath.FromSlash("data/test/second.toml"), Content: []byte("tender = 2")},
+	sources := [][2]string{
+		{filepath.FromSlash("data/test/first.toml"), "bar = 1"},
+		{filepath.FromSlash("themes/mytheme/data/test/first.toml"), "bar = 2"},
+		{filepath.FromSlash("data/test/second.toml"), "tender = 2"},
 	}
 
 	expected, _ := parser.HandleTOMLMetaData([]byte("[test.first]\nbar = 1\n[test.second]\ntender=2"))
@@ -98,7 +97,7 @@ func TestDataDirMultipleSources(t *testing.T) {
 
 }
 
-func doTestDataDir(t *testing.T, expected interface{}, sources []source.ByteSource, configKeyValues ...interface{}) {
+func doTestDataDir(t *testing.T, expected interface{}, sources [][2]string, configKeyValues ...interface{}) {
 	var (
 		cfg, fs = newTestCfg()
 	)
diff --git a/hugolib/fileInfo.go b/hugolib/fileInfo.go
new file mode 100644
index 000000000..14dd8dbf9
--- /dev/null
+++ b/hugolib/fileInfo.go
@@ -0,0 +1,109 @@
+// Copyright 2017-present The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package hugolib
+
+import (
+	"os"
+	"strings"
+
+	"github.com/gohugoio/hugo/helpers"
+	"github.com/gohugoio/hugo/source"
+)
+
+// fileInfo implements the File and ReadableFile interface.
+var (
+	_ source.File         = (*fileInfo)(nil)
+	_ source.ReadableFile = (*fileInfo)(nil)
+)
+
+type fileInfo struct {
+	bundleTp bundleDirType
+	source.ReadableFile
+	overriddenLang string
+}
+
+func (fi *fileInfo) Lang() string {
+	if fi.overriddenLang != "" {
+		return fi.overriddenLang
+	}
+	return fi.ReadableFile.Lang()
+}
+
+func (fi *fileInfo) isOwner() bool {
+	return fi.bundleTp > bundleNot
+}
+
+func isContentFile(filename string) bool {
+	return contentFileExtensionsSet[strings.TrimPrefix(helpers.Ext(filename), ".")]
+}
+
+func (fi *fileInfo) isContentFile() bool {
+	return contentFileExtensionsSet[fi.Ext()]
+}
+
+func newFileInfo(sp *source.SourceSpec, baseDir, filename string, fi os.FileInfo, tp bundleDirType) *fileInfo {
+
+	baseFi := sp.NewFileInfo(baseDir, filename, fi)
+	f := &fileInfo{
+		bundleTp:     tp,
+		ReadableFile: baseFi,
+	}
+
+	return f
+
+}
+
+type bundleDirType int
+
+const (
+	bundleNot bundleDirType = iota
+
+	// All from here are bundles in one form or another.
+	bundleLeaf
+	bundleBranch
+)
+
+// Returns the given file's name's bundle type and whether it is a content
+// file or not.
+func classifyBundledFile(name string) (bundleDirType, bool) {
+	if !isContentFile(name) {
+		return bundleNot, false
+	}
+	if strings.HasPrefix(name, "_index.") {
+		return bundleBranch, true
+	}
+
+	if strings.HasPrefix(name, "index.") {
+		return bundleLeaf, true
+	}
+
+	return bundleNot, true
+}
+
+func (b bundleDirType) String() string {
+	switch b {
+	case bundleNot:
+		return "Not a bundle"
+	case bundleLeaf:
+		return "Regular bundle"
+	case bundleBranch:
+		return "Branch bundle"
+	}
+
+	return ""
+}
+
+func (b bundleDirType) isBundle() bool {
+	return b > bundleNot
+}
diff --git a/hugolib/fileInfo_test.go b/hugolib/fileInfo_test.go
new file mode 100644
index 000000000..18579c078
--- /dev/null
+++ b/hugolib/fileInfo_test.go
@@ -0,0 +1,61 @@
+// Copyright 2017-present The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package hugolib
+
+import (
+	"testing"
+
+	"path/filepath"
+
+	"github.com/gohugoio/hugo/source"
+	"github.com/stretchr/testify/require"
+)
+
+func TestBundleFileInfo(t *testing.T) {
+	t.Parallel()
+
+	assert := require.New(t)
+	cfg, fs := newTestBundleSourcesMultilingual(t)
+	sourceSpec := source.NewSourceSpec(cfg, fs)
+
+	for _, this := range []struct {
+		filename string
+		check    func(f *fileInfo)
+	}{
+		{"/path/to/file.md", func(fi *fileInfo) {
+			assert.Equal("md", fi.Ext())
+			assert.Equal("en", fi.Lang())
+			assert.False(fi.isOwner())
+			assert.True(fi.isContentFile())
+		}},
+		{"/path/to/file.JPG", func(fi *fileInfo) {
+			assert.Equal("jpg", fi.Ext())
+			assert.False(fi.isContentFile())
+		}},
+		{"/path/to/file.nn.png", func(fi *fileInfo) {
+			assert.Equal("png", fi.Ext())
+			assert.Equal("nn", fi.Lang())
+			assert.Equal("file", fi.TranslationBaseName())
+			assert.False(fi.isContentFile())
+		}},
+	} {
+		fi := newFileInfo(
+			sourceSpec,
+			filepath.FromSlash("/work/base"),
+			filepath.FromSlash(this.filename),
+			nil, bundleNot)
+		this.check(fi)
+	}
+
+}
diff --git a/hugolib/handler_base.go b/hugolib/handler_base.go
deleted file mode 100644
index d7e4a63a3..000000000
--- a/hugolib/handler_base.go
+++ /dev/null
@@ -1,65 +0,0 @@
-// Copyright 2015 The Hugo Authors. All rights reserved.
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-// http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-package hugolib
-
-import (
-	"github.com/gohugoio/hugo/source"
-)
-
-// Handler is used for processing files of a specific type.
-type Handler interface {
-	FileConvert(*source.File, *Site) HandledResult
-	PageConvert(*Page) HandledResult
-	Read(*source.File, *Site) HandledResult
-	Extensions() []string
-}
-
-// Handle identifies functionality associated with certain file extensions.
-type Handle struct {
-	extensions []string
-}
-
-// Extensions returns a list of extensions.
-func (h Handle) Extensions() []string {
-	return h.extensions
-}
-
-// HandledResult describes the results of a file handling operation.
-type HandledResult struct {
-	page *Page
-	file *source.File
-	err  error
-}
-
-// HandledResult is an error
-func (h HandledResult) Error() string {
-	if h.err != nil {
-		if h.page != nil {
-			return "Error: " + h.err.Error() + " for " + h.page.File.LogicalName()
-		}
-		if h.file != nil {
-			return "Error: " + h.err.Error() + " for " + h.file.LogicalName()
-		}
-	}
-	return h.err.Error()
-}
-
-func (h HandledResult) String() string {
-	return h.Error()
-}
-
-// Page returns the affected page.
-func (h HandledResult) Page() *Page {
-	return h.page
-}
diff --git a/hugolib/handler_file.go b/hugolib/handler_file.go
deleted file mode 100644
index 82ea85fb2..000000000
--- a/hugolib/handler_file.go
+++ /dev/null
@@ -1,59 +0,0 @@
-// Copyright 2015 The Hugo Authors. All rights reserved.
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-// http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-package hugolib
-
-import (
-	"bytes"
-
-	"github.com/dchest/cssmin"
-	"github.com/gohugoio/hugo/source"
-)
-
-func init() {
-	RegisterHandler(new(cssHandler))
-	RegisterHandler(new(defaultHandler))
-}
-
-type basicFileHandler Handle
-
-func (h basicFileHandler) Read(f *source.File, s *Site) HandledResult {
-	return HandledResult{file: f}
-}
-
-func (h basicFileHandler) PageConvert(*Page) HandledResult {
-	return HandledResult{}
-}
-
-type defaultHandler struct{ basicFileHandler }
-
-func (h defaultHandler) Extensions() []string { return []string{"*"} }
-func (h defaultHandler) FileConvert(f *source.File, s *Site) HandledResult {
-	err := s.publish(f.Path(), f.Contents)
-	if err != nil {
-		return HandledResult{err: err}
-	}
-	return HandledResult{file: f}
-}
-
-type cssHandler struct{ basicFileHandler }
-
-func (h cssHandler) Extensions() []string { return []string{"css"} }
-func (h cssHandler) FileConvert(f *source.File, s *Site) HandledResult {
-	x := cssmin.Minify(f.Bytes())
-	err := s.publish(f.Path(), bytes.NewReader(x))
-	if err != nil {
-		return HandledResult{err: err}
-	}
-	return HandledResult{file: f}
-}
diff --git a/hugolib/handler_meta.go b/hugolib/handler_meta.go
deleted file mode 100644
index c1aaf5f8c..000000000
--- a/hugolib/handler_meta.go
+++ /dev/null
@@ -1,128 +0,0 @@
-// Copyright 2015 The Hugo Authors. All rights reserved.
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-// http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-package hugolib
-
-import (
-	"errors"
-
-	"fmt"
-
-	"github.com/gohugoio/hugo/source"
-)
-
-var handlers []Handler
-
-// MetaHandler abstracts reading and converting functionality of a Handler.
-type MetaHandler interface {
-	// Read the Files in and register
-	Read(*source.File, *Site, HandleResults)
-
-	// Generic Convert Function with coordination
-	Convert(interface{}, *Site, HandleResults)
-
-	Handle() Handler
-}
-
-// HandleResults is a channel for HandledResult.
-type HandleResults chan<- HandledResult
-
-// NewMetaHandler creates a MetaHandle for