Add nav_fixed_top option to toggle navbar-fixed-top; documentation
Added WAI-ARIA roles to layout, search, searchbox (document, navigation, banner, main, contentinfo)

https://en.wikipedia.org/wiki/WAI-ARIA

http://www.w3.org/TR/wai-aria/roles
Navbar hides initial content when jumping to in-page anchor

See https://github.com/twbs/bootstrap/issues/1768 for details.
* add badge.
* fixed flake8 warning&error.
* travis correspondence.
add .travis.yml
modfied .travis.yml
update travis.yml and badge.
add unit tests. and add coveralls's settings.
commit
commit
update travis.yml
commit
commit
commit
commit
commit
commit
commit
commit
garden