Don't explicitly reference global jQuery

Removes `window.jQuery` in favor of `jQuery`, fixes #10038
changed attr('data-target') to data('target');

this will extend js interface, to be possible to setup targets for tabs as 
    var content=$('<div class="tab-pane">',{text: 'content'});
    var tab=('<li>',{html: $('<a>',{text: 'Main options'})}).addClass('active').data({target: $main,toggle: 'tab'}).appendTo(tabs);
Add Welcome section to docs

* Fixes unrelated typo in readme
* Add new Welcome section with history, team, callouts, and community
subsections
* Redesigns callouts to be a bit lighterweight with colored headings
shorter avatar urls
use irc link
Merge branch 'master' into docs_welcome
adding required attribute for example signin form
Copy edits from @cvrebert and @juthilo
dat @juthilo edit
dat hash
move to separate about page
Dropdown in panel header does not inherit its colors

Fix for issue #10627
Removed the unnecessary override and the !important from .wrap

In the sticky footer example there were some weird stuff..
Same fix for the navbar example of sticky footer
Use bootstrap.less file order in Customizer

Appending stylesheets by iterating the `__less` Hash creates an order
that is not the same as 'bootstrap.less'.

Some stylesheets like 'component-animations.less' and 'modals.less' have
selectors with matching specificity, and so file order decides which
style wins. This causes issue #10030 by putting `.fade.in` after
`.modal-backdrop.in` and gives the backdrop a higher opacity than
intended.

This change uses the Less ordering in 'bootstrap.less' to generate the
final stylesheets in the Customizer to make sure customized file
ordering matches the distribution file order.

Fixes #10030
Disable IE Compatibility Mode in docs, examples

...because we don't support it and it may cause problems for people
trying to view the docs in IE.
Alter wording of example Skip Nav link to improve pronunciation

Screen reading applications, including Apple's VoiceOver, improperly pronounce the word "content" in "Skip to content" as an adjective rather than a noun because of insufficient context. "Skip to main content" is pronounced correctly. 

See #6 and Guideline #10 at the following site for more information:
http://redish.net/content/papers/interactions.htmlAlter wording of example Skip Nav link to improve pronunciation
Add note about IE mode tag being included in docs
Merge pull request #10790 from twbs/disable-compatibility-mode

Disable IE Compatibility Mode in docs, examples
Merge pull request #10786 from acspike/skip-nav-link-wording

Alter wording of example Skip Nav link to improve pronunciation