This PR significantly improves Bootstrap's accessibility for users of assistive technology, such as screen readers. Some of the these changes add additional markup to the source examples, but we believe that the sacrifice in readability is worth achieving more widespread usage of accessibility best-practices.

What was done
- Added lots of [WAI-ARIA attributes](http://www.w3.org/WAI/intro/aria)
- Added `.sr-only` helper class, that is only readable by screen readers (and invisible for all other users). This lets us - make progress bars and paginations accessible to screen reading users.
- Advised users to always use label elements. For inline forms, they can hide them with `.sr-only`
- Added 'Skip navigation' link
- Added "Accessibility" section to getting-started.html.

What *wasn't* done
- Contrast issues (twbs#3572)
- Tooltips (twbs#8469)
- Documentation re: usage of icons, since they now live in a separate repo

Major props to all that contributed: @bensheldon, @jasonlally, @criscristina, and @louh. Feel free to chime in, guys, if I've left anything out.

fixes #8959: only negative indent rows within .container (prevents horizontal scroll on full-width pages)

disable BrowserStack for folks w/o their own key who are making PRs

fix scrollSpy instructions for JS call

Conflicts:
	less/mixins.less

Per @mdo's request.
Can re-enable IE after @fat figures out wassup w/ the unittest failures.

BS3: Add third party support docs

/cc @cv

Fixes #9162: add mention of Windows Phone 8 and IE10 bugs with responsive foo

Format multiple badges in list-group-item

Fix spacing after '=' in popover.js

Just added a space after a function definition to tidy up the code.

Browserstack testing integration (rebased, squashed, tweaked)

People, don't PR against `gh-pages` please!

Update tooltips to not use RGBa colors so IE8 can have tooltips, too
(means we're now using `opacity`).

Properly hides popover titles in IE8 because apparently it doesn't
accept the `:empty` selector. /cc @fat @cvrebert

Add links to Recess, Uglify-js & PhantomJS in README