Add helper classes for accessibility and invisible, focusable skip link.
Merge pull request #9 from davidakennedy/skip-link

Add helper classes for accessibility and invisible, focusable skip link.
Add ARIA roles to header, nav and footer.
Merge pull request #10 from davidakennedy/aria

Add ARIA roles to header, nav and footer.
include Dave in the list of contributors
alphabetize contributors and remind folks to add themselves to the list
missing .