rename classes from .bs-docs and .bs to .bd

docs/getting-started/accessibility.md

@@ -9,7 +9,7 @@ Bootstrap follows common web standards and—with minimal extra effort—can be
 
 If your navigation contains many links and comes before the main content in the DOM, add a `Skip to main content` link before the navigation (for a simple explanation, see this [A11Y Project article on skip navigation links](http://a11yproject.com/posts/skip-nav-links/)). Using the `.sr-only` class will visually hide the skip link, and the <code>.sr-only-focusable</code> class will ensure that the link becomes visible once focused (for sighted keyboard users).
 
-<div class="bs-callout bs-callout-danger" id="callout-skiplinks">
+<div class="bd-callout bd-callout-danger" id="callout-skiplinks">
   <p>Due to long-standing shortcomings/bugs in Chrome (see <a href="https://code.google.com/p/chromium/issues/detail?id=262171" title="Chromium bug tracker - Issue 262171: Focus should cycle from named anchor">issue 262171 in the Chromium bug tracker</a>) and Internet Explorer (see this article on <a href="http://accessibleculture.org/articles/2010/05/in-page-links/">in-page links and focus order</a>), you will need to make sure that the target of your skip link is at least programmatically focusable by adding <code>tabindex="-1"</code>.</p>
   <p>In addition, you may want to explicitly suppress a visible focus indication on the target (particularly as Chrome currently also sets focus on elements with <code>tabindex="-1"</code> when they are clicked with the mouse) with <code>#content:focus { outline: none; }</code>.</p>
   <p>Note that this bug will also affect any other in-page links your site may be using, rendering them useless for keyboard users. You may consider adding a similar stop-gap fix to all other named anchors / fragment identifiers that act as link targets.</p>