: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, 15 insertions, 16 deletions

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()
 	)