🎁I 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).

Fixes gohugoio#3651
Closes gohugoio#3158
Fixes gohugoio#1014
Closes gohugoio#2021
Fixes gohugoio#1240
Updates gohugoio#3757

Author: bep

Diff for: Gopkg.lock

@@ -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"
 
 [[constraint]]
   name = "github.com/magefile/mage"
@@ -116,6 +116,10 @@
   name = "github.com/stretchr/testify"
   version = "1.1.4"
 
+[[constraint]]
+  branch = "master"
+  name = "github.com/olekukonko/tablewriter"
+
 [[constraint]]
   name = "github.com/yosssi/ace"
   version = "0.0.5"