Merge pull request #18 from ericf/mobile-first

Added html5shiv and Grunt watch task
update media query to be 48em
update pricing layout to be mobile-first
update side-menu layout to be mobile-first
update marketing page to be mobile-first, update design
update gallery layout to be mobile-first, use new images
update email layout to be mobile-first
update Gruntfile with layout tasks
remove `pure-` prefix from classes that are not part of Pure core
px -> em, add `.pure-img-responsive` class for now
write `id` attribute before `class` :)
add "forms" to marketing meta
update blog layout colors & image
fix `.header h2` being too light
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