: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, 101 insertions, 0 deletions

diff --git a/hugolib/site_stats_test.go b/hugolib/site_stats_test.go
new file mode 100644
index 000000000..522b5636b
--- /dev/null
+++ b/hugolib/site_stats_test.go
@@ -0,0 +1,101 @@
+// Copyright 2017 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 hugolib
+
+import (
+	"bytes"
+	"fmt"
+	"io/ioutil"
+	"testing"
+
+	"github.com/gohugoio/hugo/helpers"
+	"github.com/spf13/afero"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestSiteStats(t *testing.T) {
+	t.Parallel()
+
+	assert := require.New(t)
+
+	siteConfig := `
+baseURL = "http://example.com/blog"
+
+paginate = 1
+defaultContentLanguage = "nn"
+
+[languages]
+[languages.nn]
+languageName = "Nynorsk"
+weight = 1
+title = "Hugo på norsk"
+
+[languages.en]
+languageName = "English"
+weight = 2
+title = "Hugo in English"
+
+`
+
+	pageTemplate := `---
+title: "T%d"
+tags:
+%s
+categories:
+%s
+aliases: [Ali%d]
+---
+# Doc
+`
+
+	th, h := newTestSitesFromConfig(t, afero.NewMemMapFs(), siteConfig,
+		"layouts/_default/single.html", "Single|{{ .Title }}|{{ .Content }}",
+		"layouts/_default/list.html", `List|{{ .Title }}|Pages: {{ .Paginator.TotalPages }}|{{ .Content }}`,
+		"layouts/_default/terms.html", "Terms List|{{ .Title }}|{{ .Content }}",
+	)
+	require.Len(t, h.Sites, 2)
+
+	fs := th.Fs
+
+	for i := 0; i < 2; i++ {
+		for j := 0; j < 2; j++ {
+			pageID := i + j + 1
+			writeSource(t, fs, fmt.Sprintf("content/sect/p%d.md", pageID),
+				fmt.Sprintf(pageTemplate, pageID, fmt.Sprintf("- tag%d", j), fmt.Sprintf("- category%d", j), pageID))
+		}
+	}
+
+	for i := 0; i < 5; i++ {
+		writeSource(t, fs, fmt.Sprintf("content/assets/image%d.png", i+1), "image")
+	}
+
+	err := h.Build(BuildCfg{})
+
+	assert.NoError(err)
+
+	stats := []*helpers.ProcessingStats{
+		h.Sites[0].PathSpec.ProcessingStats,
+		h.Sites[1].PathSpec.ProcessingStats}
+
+	stats[0].Table(ioutil.Discard)
+	stats[1].Table(ioutil.Discard)
+
+	var buff bytes.Buffer
+
+	helpers.ProcessingStatsTable(&buff, stats...)
+
+	assert.Contains(buff.String(), "Pages            | 19 |  6")
+
+}