Basic keyboard accessibility CSS tweaks

Mostly doubling-up :hover styles to also cover :focus, as a first step
to making the framework more keyboard-friendly.
Additionally, fixed two small markup issues in the docs/examples to
make the "Learn more" large primary button-styled links
keyboard-focusable (as without href they're treated as non-tabable
anchors).
Cleaned up dirty CSS

Used recess rather than less
Keyboard accessibility in documentation

Removed unnecessary (?) and harmful (from a keyboard access point of
view) tabindex=-1 in the documentation examples.
Revert "Keyboard accessibility in documentation"

This reverts commit a809daf2841f65ffac5030b2c6ce6aea60dd6233.
Leave tabindex=-1 alone

It seems that, as misguided as I personally think it is, ARIA does
indeed want dropdown menus not to behave as regular keyboard users
expect them, killing TAB/SHIFT+TAB in favor of cursor keys. Fair
enough, the issue I have is then with ARIA, not with bootstrap. I would
sugges thought that if you really do want to follow ARIA consistently,
*any* navigation bar should also become an ARIA menu, further making it
impossible for keyboard users to use TAB/SHIFT+TAB to navigate through
it, and that these changes should be reflected in the bootstrap
examples as well...
Revert "Leave tabindex=-1 alone"

This reverts commit 370fa45fbe4ee879a626a67bb4df0ec9495102be.
Merge branch '2.3.0-wip' of https://github.com/patrickhlauke/bootstrap into patrickhlauke-2.3.0-wip

Conflicts:
	docs/assets/css/bootstrap.css
	less/navbar.less
restore comma between selectors
derp, fix broke css and recompile
Merge branch '2.3.0-wip' of github.com:twitter/bootstrap into 2.3.0-wip