: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, 9 insertions, 37 deletions

diff --git a/helpers/path.go b/helpers/path.go
index 57f02da68..44d53d018 100644
--- a/helpers/path.go
+++ b/helpers/path.go
@@ -277,6 +277,12 @@ func Ext(in string) string {
 	return ext
 }
 
+// FileAndExt takes a path and returns the file and extension separated,
+// the extension including the delmiter, i.e. ".md".
+func FileAndExt(in string) (string, string) {
+	return fileAndExt(in, fpb)
+}
+
 // Filename takes a path, strips out the extension,
 // and returns the name of the file.
 func Filename(in string) (name string) {
@@ -348,40 +354,6 @@ func GetRelativePath(path, base string) (final string, err error) {
 	return name, nil
 }
 
-// GuessSection returns the section given a source path.
-// A section is the part between the root slash and the second slash
-// or before the first slash.
-func GuessSection(in string) string {
-	parts := strings.Split(in, FilePathSeparator)
-	// This will include an empty entry before and after paths with leading and trailing slashes
-	// eg... /sect/one/ -> ["", "sect", "one", ""]
-
-	// Needs to have at least a value and a slash
-	if len(parts) < 2 {
-		return ""
-	}
-
-	// If it doesn't have a leading slash and value and file or trailing slash, then return ""
-	if parts[0] == "" && len(parts) < 3 {
-		return ""
-	}
-
-	// strip leading slash
-	if parts[0] == "" {
-		parts = parts[1:]
-	}
-
-	// if first directory is "content", return second directory
-	if parts[0] == "content" {
-		if len(parts) > 2 {
-			return parts[1]
-		}
-		return ""
-	}
-
-	return parts[0]
-}
-
 // PathPrep prepares the path using the uglify setting to create paths on
 // either the form /section/name/index.html or /section/name.html.
 func PathPrep(ugly bool, in string) string {
@@ -504,7 +476,7 @@ func SymbolicWalk(fs afero.Fs, root string, walker filepath.WalkFunc) error {
 }
 
 func getRealFileInfo(fs afero.Fs, path string) (os.FileInfo, string, error) {
-	fileInfo, err := lstatIfOs(fs, path)
+	fileInfo, err := LstatIfOs(fs, path)
 	realPath := path
 
 	if err != nil {
@@ -516,7 +488,7 @@ func getRealFileInfo(fs afero.Fs, path string) (os.FileInfo, string, error) {
 		if err != nil {
 			return nil, "", fmt.Errorf("Cannot read symbolic link '%s', error was: %s", path, err)
 		}
-		fileInfo, err = lstatIfOs(fs, link)
+		fileInfo, err = LstatIfOs(fs, link)
 		if err != nil {
 			return nil, "", fmt.Errorf("Cannot stat '%s', error was: %s", link, err)
 		}
@@ -539,7 +511,7 @@ func GetRealPath(fs afero.Fs, path string) (string, error) {
 
 // Code copied from Afero's path.go
 // if the filesystem is OsFs use Lstat, else use fs.Stat
-func lstatIfOs(fs afero.Fs, path string) (info os.FileInfo, err error) {
+func LstatIfOs(fs afero.Fs, path string) (info os.FileInfo, err error) {
 	_, ok := fs.(*afero.OsFs)
 	if ok {
 		info, err = os.Lstat(path)