footer is now connected to nav, many other changes here

- No more ids in styles (were provisional anyway, now no longer needed)
- Nav no longer contained in a "section" (unnecessary)
- Updated footer language
- Footer now has a light background instead of being part of the dark
site background
- At smaller screen sizes, footer and .site-nav are now flush
- .site-nav no longer uses .page styles
.site-nav once again scales with .page and .banner at > 30em
CSS refactoring after .site-nav changes
Merge pull request #34 from opattison/new-footer-style

New footer style (resolves #33)