: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, 108 insertions, 0 deletions

diff --git a/resource/resource_test.go b/resource/resource_test.go
new file mode 100644
index 000000000..34d63cd60
--- /dev/null
+++ b/resource/resource_test.go
@@ -0,0 +1,108 @@
+// 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 resource
+
+import (
+	"path"
+	"path/filepath"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestGenericResource(t *testing.T) {
+	assert := require.New(t)
+	spec := newTestResourceSpec(assert)
+
+	r := spec.newGenericResource(nil, nil, "/public", "/a/foo.css", "foo.css", "css")
+
+	assert.Equal("https://example.com/foo.css", r.Permalink())
+	assert.Equal("foo.css", r.RelPermalink())
+	assert.Equal("css", r.ResourceType())
+
+}
+
+func TestGenericResourceWithLinkFacory(t *testing.T) {
+	assert := require.New(t)
+	spec := newTestResourceSpec(assert)
+
+	factory := func(s string) string {
+		return path.Join("/foo", s)
+	}
+	r := spec.newGenericResource(factory, nil, "/public", "/a/foo.css", "foo.css", "css")
+
+	assert.Equal("https://example.com/foo/foo.css", r.Permalink())
+	assert.Equal("/foo/foo.css", r.RelPermalink())
+	assert.Equal("css", r.ResourceType())
+}
+
+func TestNewResourceFromFilename(t *testing.T) {
+	assert := require.New(t)
+	spec := newTestResourceSpec(assert)
+
+	writeSource(t, spec.Fs, "/project/a/b/logo.png", "image")
+	writeSource(t, spec.Fs, "/root/a/b/data.json", "json")
+
+	r, err := spec.NewResourceFromFilename(nil, "/public",
+		filepath.FromSlash("/project/a/b/logo.png"), filepath.FromSlash("a/b/logo.png"))
+
+	assert.NoError(err)
+	assert.NotNil(r)
+	assert.Equal("image", r.ResourceType())
+	assert.Equal("a/b/logo.png", r.RelPermalink())
+	assert.Equal("https://example.com/a/b/logo.png", r.Permalink())
+
+	r, err = spec.NewResourceFromFilename(nil, "/public", "/root/a/b/data.json", "a/b/data.json")
+
+	assert.NoError(err)
+	assert.NotNil(r)
+	assert.Equal("json", r.ResourceType())
+
+	cloned := r.(Cloner).WithNewBase("aceof")
+	assert.Equal(r.ResourceType(), cloned.ResourceType())
+	assert.Equal("/aceof/a/b/data.json", cloned.RelPermalink())
+}
+
+func TestResourcesByType(t *testing.T) {
+	assert := require.New(t)
+	spec := newTestResourceSpec(assert)
+	resources := Resources{
+		spec.newGenericResource(nil, nil, "/public", "/a/foo1.css", "foo1.css", "css"),
+		spec.newGenericResource(nil, nil, "/public", "/a/logo.png", "logo.css", "image"),
+		spec.newGenericResource(nil, nil, "/public", "/a/foo2.css", "foo2.css", "css"),
+		spec.newGenericResource(nil, nil, "/public", "/a/foo3.css", "foo3.css", "css")}
+
+	assert.Len(resources.ByType("css"), 3)
+	assert.Len(resources.ByType("image"), 1)
+
+}
+
+func TestResourcesGetByPrefix(t *testing.T) {
+	assert := require.New(t)
+	spec := newTestResourceSpec(assert)
+	resources := Resources{
+		spec.newGenericResource(nil, nil, "/public", "/a/foo1.css", "foo1.css", "css"),
+		spec.newGenericResource(nil, nil, "/public", "/a/logo1.png", "logo1.png", "image"),
+		spec.newGenericResource(nil, nil, "/public", "/b/logo2.png", "logo2.png", "image"),
+		spec.newGenericResource(nil, nil, "/public", "/b/foo2.css", "foo2.css", "css"),
+		spec.newGenericResource(nil, nil, "/public", "/b/foo3.css", "foo3.css", "css")}
+
+	assert.Nil(resources.GetByPrefix("asdf"))
+	assert.Equal("logo1.png", resources.GetByPrefix("logo").RelPermalink())
+	assert.Equal("foo2.css", resources.GetByPrefix("foo2").RelPermalink())
+	assert.Equal("foo1.css", resources.GetByPrefix("foo1").RelPermalink())
+	assert.Equal("foo1.css", resources.GetByPrefix("foo1").RelPermalink())
+	assert.Nil(resources.GetByPrefix("asdfasdf"))
+
+}