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
fix #10767; current .img-thumbnail is equivalent to old .img-polaroid
deprecate .hide; fixes #10446
move /assets/ to /docs-assets/ ; fixes #10715
avoid using the term "assets" due to potential confusion
Merge pull request #10769 from twbs/deprecate-hide

deprecate .hide; fixes #10446
Merge pull request #10770 from twbs/rename-assets

move /assets/ to /docs-assets/ ; fixes #10715