Refactor highlighting

Extract some of the common logic from the renderers.
Context is not used within any of the renders so no need to pass it
Revert back to an intialize more similar to the original
Merge pull request #2154 from jpiasetz/refactor-highlighter
Update history to reflect merge of #2154 [ci skip]
Update util functions

Cribbed from http://api.rubyonrails.org/classes/Hash.html#method-i-symbolize_keys
Merge pull request #2273 from jpiasetz/copy-rails-functions
Update history to reflect merge of #2273 [ci skip]
Update URL for jekyll-help repo
Merge pull request #2277 from troyswanson/jekyll-help-relocation
Update history to reflect merge of #2277 [ci skip]
Add an 'unreleased' note above Front-matter defaults.

Fixes #2280.
Move vendor prefixed properties before the unprefixed ones.
Use the shorthand font property when possible.

Conflicts:
	site/_includes/css/style.css
Be explicit with the `background` property.
Remove units from zero.
Remove duplicate properties.
Add fallback colors.
Add missing vendor prefixed properties.
Simplify selectors.