Tweak main layout and footer/legal styles

This also adds `pure-u-sm-*` grid units.
Update copyright year to 2014
Improve Handlebars helpers: {{code}}, {{fileSize}}, and {{filePercent}}
Update Grids breakpoints to: 35.5, 48, 58, and 75em
Completely refactor CSS to truly be mobile/content-first
Update header heading styles
Use `-webkit-overflow-scrolling: touch;` for smooth scrolling
Make Pure Paginator Buttons `box-sizing: content-box;`
Add more spacing for labels on Grids unit sizes chart
Merge pull request #19 from ericf/mobile-first

Big refactor of CSS to truly be mobile/content-first