Add basic layout to all cheat sheet markdown
Add cheat-sheet layout for remaining docs
Add first pass multi-column "PDF" style appearance
Add YAML front matter title, byline

Provides anticipated fields for layout templates for web page rendering.
Force main title, byline hidden by template layout
Tune cheat sheet footer styles
Merge pull request #252 from github/cheat-sheet-page-styles

Support web-base HTML layout for cheat sheet markdown