: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

85 files changed, 5747 insertions, 3243 deletions

diff --git a/Gopkg.lock b/Gopkg.lock
index 4233d9278..44f957d18 100644
--- a/Gopkg.lock
+++ b/Gopkg.lock
@@ -21,7 +21,13 @@
 
 [[projects]]
   name = "github.com/alecthomas/chroma"
-  packages = [".","formatters","formatters/html","lexers","styles"]
+  packages = [
+    ".",
+    "formatters",
+    "formatters/html",
+    "lexers",
+    "styles"
+  ]
   revision = "v0.2.0"
 
 [[projects]]
@@ -54,21 +60,26 @@
   version = "v1.1.0"
 
 [[projects]]
-  branch = "master"
-  name = "github.com/dchest/cssmin"
+  name = "github.com/disintegration/imaging"
   packages = ["."]
-  revision = "fb8d9b44afdc258bfff6052d3667521babcb2239"
+  revision = "v1.2.4"
 
 [[projects]]
   name = "github.com/dlclark/regexp2"
-  packages = [".","syntax"]
+  packages = [
+    ".",
+    "syntax"
+  ]
   revision = "487489b64fb796de2e55f4e8a4ad1e145f80e957"
   version = "v1.1.6"
 
 [[projects]]
   branch = "master"
   name = "github.com/eknkc/amber"
-  packages = [".","parser"]
+  packages = [
+    ".",
+    "parser"
+  ]
   revision = "cdade1c073850f4ffc70a829e31235ea6892853b"
 
 [[projects]]
@@ -104,7 +115,17 @@
 [[projects]]
   branch = "master"
   name = "github.com/hashicorp/hcl"
-  packages = [".","hcl/ast","hcl/parser","hcl/scanner","hcl/strconv","hcl/token","json/parser","json/scanner","json/token"]
+  packages = [
+    ".",
+    "hcl/ast",
+    "hcl/parser",
+    "hcl/scanner",
+    "hcl/strconv",
+    "hcl/token",
+    "json/parser",
+    "json/scanner",
+    "json/token"
+  ]
   revision = "23c074d0eceb2b8a5bfdbb271ab780cde70f05a8"
 
 [[projects]]
@@ -115,7 +136,10 @@
 
 [[projects]]
   name = "github.com/jdkato/prose"
-  packages = ["internal/util","transform"]
+  packages = [
+    "internal/util",
+    "transform"
+  ]
   revision = "20d3663d4bc9dd10d75abcde9d92e04b4861c674"
   version = "v1.1.0"
 
@@ -133,7 +157,10 @@
 
 [[projects]]
   name = "github.com/magefile/mage"
-  packages = ["mg","sh"]
+  packages = [
+    "mg",
+    "sh"
+  ]
   revision = "2f974307b636f59c13b88704cf350a4772fef271"
   version = "v1.0.2"
 
@@ -150,6 +177,12 @@
   revision = "54ffb37507cd7d2ccd4768855e84f9ff6c4352b6"
 
 [[projects]]
+  name = "github.com/mattn/go-runewidth"
+  packages = ["."]
+  revision = "9e777a8366cce605130a531d2cd6363d07ad7317"
+  version = "v0.0.2"
+
+[[projects]]
   name = "github.com/miekg/mmark"
   packages = ["."]
   revision = "fd2f6c1403b37925bd7fe13af05853b8ae58ee5f"
@@ -163,11 +196,21 @@
 
 [[projects]]
   name = "github.com/nicksnyder/go-i18n"
-  packages = ["i18n/bundle","i18n/language","i18n/translation"]
+  packages = [
+    "i18n/bundle",
+    "i18n/language",
+    "i18n/translation"
+  ]
   revision = "0dc1626d56435e9d605a29875701721c54bc9bbd"
   version = "v1.10.0"
 
 [[projects]]
+  branch = "master"
+  name = "github.com/olekukonko/tablewriter"
+  packages = ["."]
+  revision = "65fec0d89a572b4367094e2058d3ebe667de3b60"
+
+[[projects]]
   name = "github.com/pelletier/go-toml"
   packages = ["."]
   revision = "16398bac157da96aa88f98a2df640c7f32af1da2"
@@ -193,7 +236,10 @@
 
 [[projects]]
   name = "github.com/spf13/afero"
-  packages = [".","mem"]
+  packages = [
+    ".",
+    "mem"
+  ]
   revision = "8d919cbe7e2627e417f3e45c3c0e489a5b7e2536"
   version = "v1.0.0"
 
@@ -206,7 +252,10 @@
 [[projects]]
   branch = "master"
   name = "github.com/spf13/cobra"
-  packages = [".","doc"]
+  packages = [
+    ".",
+    "doc"
+  ]
   revision = "7b2c5ac9fc04fc5efafb60700713d4fa609b777b"
 
 [[projects]]
@@ -241,7 +290,10 @@
 
 [[projects]]
   name = "github.com/stretchr/testify"
-  packages = ["assert","require"]
+  packages = [
+    "assert",
+    "require"
+  ]
   revision = "69483b4bd14f5845b5a1e55bca19e954e827f1d0"
   version = "v1.1.4"
 
@@ -254,17 +306,34 @@
 [[projects]]
   branch = "master"
   name = "golang.org/x/image"
-  packages = ["riff","vp8","vp8l","webp"]
+  packages = [
+    "bmp",
+    "riff",
+    "tiff",
+    "tiff/lzw",
+    "vp8",
+    "vp8l",
+    "webp"
+  ]
   revision = "f7e31b4ea2e3413ab91b4e7d2dc83e5f8d19a44c"
 
 [[projects]]
   branch = "master"
   name = "golang.org/x/net"
-  packages = ["idna"]
+  packages = [
+    "context",
+    "idna"
+  ]
   revision = "cd69bc3fc700721b709c3a59e16e24c67b58f6ff"
 
 [[projects]]
   branch = "master"
+  name = "golang.org/x/sync"
+  packages = ["errgroup"]
+  revision = "fd80eb99c8f653c847d294a001bdf2a3a6f768f5"
+
+[[projects]]
+  branch = "master"
   name = "golang.org/x/sys"
   packages = ["unix"]
   revision = "8dbc5d05d6edcc104950cc299a1ce6641235bc86"
@@ -272,7 +341,23 @@
 [[projects]]
   branch = "master"
   name = "golang.org/x/text"
-  packages = ["collate","collate/build","internal/colltab","internal/gen","internal/tag","internal/triegen","internal/ucd","language","secure/bidirule","transform","unicode/bidi","unicode/cldr","unicode/norm","unicode/rangetable","width"]
+  packages = [
+    "collate",
+    "collate/build",
+    "internal/colltab",
+    "internal/gen",
+    "internal/tag",
+    "internal/triegen",
+    "internal/ucd",
+    "language",
+    "secure/bidirule",
+    "transform",
+    "unicode/bidi",
+    "unicode/cldr",
+    "unicode/norm",
+    "unicode/rangetable",
+    "width"
+  ]
   revision = "c01e4764d870b77f8abe5096ee19ad20d80e8075"
 
 [[projects]]
@@ -284,6 +369,6 @@
 [solve-meta]
   analyzer-name = "dep"
   analyzer-version = 1
-  inputs-digest = "d75b02c8a7c7d724120447dd438e7bef140d0f4d4986adda52eabbfe3db8271a"
+  inputs-digest = "2d9c34c260bc26814a0635c93009daeb9d8ffa56c29c0cff6827ae2d3e9ef96d"
   solver-name = "gps-cdcl"
   solver-version = 1
diff --git a/Gopkg.toml b/Gopkg.toml
index c8f192974..cef7427ce 100644
--- a/Gopkg.toml
+++ b/Gopkg.toml
@@ -21,8 +21,8 @@
  revision = "v1.1.0"
 
 [[constraint]]
-  branch = "master"
-  name = "github.com/dchest/cssmin"
+ name = "github.com/disintegration/imaging"
+ revision = "v1.2.4"