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.