: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

1 files changed, 0 insertions, 62 deletions

diff --git a/source/file_test.go b/source/file_test.go
deleted file mode 100644
index 64ad6fb46..000000000
--- a/source/file_test.go
+++ /dev/null
@@ -1,62 +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 source
-
-import (
-	"path/filepath"
-	"strings"
-	"testing"
-
-	"github.com/gohugoio/hugo/hugofs"
-	"github.com/spf13/viper"
-
-	"github.com/stretchr/testify/assert"
-)
-
-func TestFileUniqueID(t *testing.T) {
-	ss := newTestSourceSpec()
-
-	f1 := File{uniqueID: "123"}
-	f2 := ss.NewFile("a")
-
-	assert.Equal(t, "123", f1.UniqueID())
-	assert.Equal(t, "0cc175b9c0f1b6a831c399e269772661", f2.UniqueID())
-
-	f3 := ss.NewFile(filepath.FromSlash("test1/index.md"))
-	f4 := ss.NewFile(filepath.FromSlash("test2/index.md"))
-
-	assert.NotEqual(t, f3.UniqueID(), f4.UniqueID())
-
-	f5l := ss.NewFile("test3/index.md")
-	f5w := ss.NewFile(filepath.FromSlash("test3/index.md"))
-
-	assert.Equal(t, f5l.UniqueID(), f5w.UniqueID())
-}
-
-func TestFileString(t *testing.T) {
-	ss := newTestSourceSpec()
-	assert.Equal(t, "abc", ss.NewFileWithContents("a", strings.NewReader("abc")).String())
-	assert.Equal(t, "", ss.NewFile("a").String())
-}
-
-func TestFileBytes(t *testing.T) {
-	ss := newTestSourceSpec()
-	assert.Equal(t, []byte("abc"), ss.NewFileWithContents("a", strings.NewReader("abc")).Bytes())
-	assert.Equal(t, []byte(""), ss.NewFile("a").Bytes())
-}
-
-func newTestSourceSpec() SourceSpec {
-	v := viper.New()
-	return SourceSpec{Fs: hugofs.NewMem(v), Cfg: v}
-}