: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, 7 insertions, 27 deletions

diff --git a/hugolib/hugo_sites_build.go b/hugolib/hugo_sites_build.go
index c0749e388..b2b394eb5 100644
--- a/hugolib/hugo_sites_build.go
+++ b/hugolib/hugo_sites_build.go
@@ -15,7 +15,6 @@ package hugolib
 
 import (
 	"bytes"
-	"time"
 
 	"errors"
 
@@ -30,7 +29,7 @@ func (h *HugoSites) Build(config BuildCfg, events ...fsnotify.Event) error {
 		h.Metrics.Reset()
 	}
 
-	t0 := time.Now()
+	//t0 := time.Now()
 
 	// Need a pointer as this may be modified.
 	conf := &config
@@ -63,10 +62,6 @@ func (h *HugoSites) Build(config BuildCfg, events ...fsnotify.Event) error {
 		return err
 	}
 
-	if config.PrintStats {
-		h.Log.FEEDBACK.Printf("total in %v ms\n", int(1000*time.Since(t0).Seconds()))
-	}
-
 	if h.Metrics != nil {
 		var b bytes.Buffer
 		h.Metrics.WriteMetrics(&b)
@@ -101,8 +96,6 @@ func (h *HugoSites) init(config *BuildCfg) error {
 		}
 	}
 
-	h.runMode.Watching = config.Watching
-
 	return nil
 }
 
@@ -115,12 +108,10 @@ func (h *HugoSites) initRebuild(config *BuildCfg) error {
 		return errors.New("Rebuild does not support 'ResetState'.")
 	}
 
-	if !config.Watching {
+	if !h.running {
 		return errors.New("Rebuild called when not in watch mode")
 	}
 
-	h.runMode.Watching = config.Watching
-
 	if config.whatChanged.source {
 		// This is for the non-renderable content pages (rarely used, I guess).
 		// We could maybe detect if this is really needed, but it should be
@@ -147,7 +138,7 @@ func (h *HugoSites) process(config *BuildCfg, events ...fsnotify.Event) error {
 
 	if len(events) > 0 {
 		// This is a rebuild
-		changed, err := firstSite.reProcess(events)
+		changed, err := firstSite.processPartial(events)
 		config.whatChanged = &changed
 		return err
 	}
@@ -188,25 +179,19 @@ func (h *HugoSites) assemble(config *BuildCfg) error {
 	}
 
 	for _, s := range h.Sites {
-		s.siteStats = &siteStats{}
 		for _, p := range s.Pages {
 			// May have been set in front matter
 			if len(p.outputFormats) == 0 {
 				p.outputFormats = s.outputFormats[p.Kind]
 			}
-
-			cnt := len(p.outputFormats)
-			if p.Kind == KindPage {
-				s.siteStats.pageCountRegular += cnt
+			for _, r := range p.Resources.ByType(pageResourceType) {
+				r.(*Page).outputFormats = p.outputFormats
 			}
-			s.siteStats.pageCount += cnt
 
-			if err := p.initTargetPathDescriptor(); err != nil {
-				return err
-			}
-			if err := p.initURLs(); err != nil {
+			if err := p.initPaths(); err != nil {
 				return err
 			}
+
 		}
 		s.assembleMenus()
 		s.refreshPageCaches()
@@ -222,7 +207,6 @@ func (h *HugoSites) assemble(config *BuildCfg) error {
 }
 
 func (h *HugoSites) render(config *BuildCfg) error {
-
 	for _, s := range h.Sites {
 		s.initRenderFormats()
 		for i, rf := range s.renderFormats {
@@ -235,10 +219,6 @@ func (h *HugoSites) render(config *BuildCfg) error {
 				}
 			}
 		}
-
-		if !config.SkipRender && config.PrintStats {
-			s.Stats()
-		}
 	}
 
 	if !config.SkipRender {