Toggle table of contents via front matter (#1310)

* Add jekyll-toc include
* Reduce whitespace generated by comments
* Add table of contents include to `single` layout
* Replace `toc` include with jekyll-toc enabled YAML Front Matter
* Update README
* Update table of contents documentation
  - Revise `toc` helper include to mention that it will be deprecated in the next major version.
  - Add documentation to `single` layout explaining how to enable table of contents on those pages.
* Update CHANGELOG and history
* Update LICENSE

Close #1222

docs/_posts/2016-10-06-gemified-theme-beta.md

@@ -1,16 +1,16 @@
 ---
 title:  "Gemified Theme -- Beta Release"
-last_modified_at: 2016-11-03T11:45:04-04:00
+last_modified_at: 2017-10-20T12:29:16-04:00
 categories: 
   - Jekyll
 tags:
   - update
+toc: true
+toc_label: "Getting Started"
 ---
 
 Hot on the heels of Jekyll v3.3.0 is a beta release of Minimal Mistakes... as a gemified theme.
 
-{% include toc title="Getting Started" %}
-
 [`minimal-mistakes-jekyll`](https://rubygems.org/gems/minimal-mistakes-jekyll) can only be used with Jekyll proper. If you're hosting on GitHub Pages or using that gem the theme won't work. 3rd party themes haven't been white-listed so it's a no go for now.
 
 Fine with all that? Great. Let's continue.