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/2016-09-21-gemified-theme-alpha.md

@@ -1,16 +1,16 @@
 ---
 title:  "Gemified Theme -- Alpha Release"
-last_modified_at: 2016-11-03T11:46:00-04:00
+last_modified_at: 2017-10-20T12:29:34-04:00
 categories: 
   - Jekyll
 tags:
   - update
+toc: true
+toc_label: "Getting Started"
 ---
 
 Jekyll [themes distributed as Ruby gems](http://jekyllrb.com/docs/themes/) are finally here to make installing and upgrading much easier. Gone are the days of forking a repo just to "install it". Or dealing with merge conflicts when pulling in upstream commits to "upgrade it".
 
-{% include toc title="Getting Started" %}
-
 If you're interested in testing out Minimal Mistakes as a gemified theme read on. There are a few caveats though:
 
 1. Support for a theme `assets` folder was recently [added to Jekyll core](https://github.com/jekyll/jekyll/pull/5364), but has yet to be released or rolled into the `github-pages` gem. Meaning you can't use Minimal Mistakes as a Ruby gem there just yet... locally served or self-hosted installs should be fine if you don't mind using a pre-release version of Jekyll.