Add `toc_sticky` to stick table of contents

"Stick" table of contents to top of the page by adding:

```
toc: true
toc_sticky: true
```

to a post or page's YAML Front Matter.
Note: only supported with `single` layout.

Add support for captioning images in feature row helper

Use `image_caption` YAML front matter to assign a caption to the feature image, Markdown is allowed.

Close #1440

Update CHANGELOG and history

Merge branch 'master' of https://github.com/mmistakes/minimal-mistakes

Implement feature #1652 google custom search support.  (#1667)

Implement feature #1652 google custom search support. For now we only support the look and feel "results only" and the engine must be set to use that layout. Add a google section to the search providers and search_form and search layout.

Close #1652

Fix table of contents missing borders

Fixes #1675

Update CHANGELOG and history

update Font Awesome (#1668)

REF: https://github.com/FortAwesome/Font-Awesome/blob/master/CHANGELOG.md

Update CHANGELOG and history

Update CHANGELOG and history

#1659: Prevent line breaking between icon & text in footer social links (#1660)

Update CHANGELOG and history

Update CHANGELOG and history

#1653: Add GitLab social icon brand color (#1654)

Fix "Back to Top" links

Pages that use header overlays were missing `#page-title` anchors on the `<h1>` element.

Release 4.11.2 :gem:

Update Font Awesome to 5.0.12

Update CHANGELOG and history

Add option to anonymize analytics ip address (#1636)

* Add option to anonymize analytics ip address

* Add option to anonymize analytics ip address in google tag

Update Font Awesome to v5.0.11 (#1620)

* Update Font Awesome to v5.0.10

https://github.com/FortAwesome/Font-Awesome/blob/master/CHANGELOG.md

* Update scripts.html