correct enable selector for button usage

following the given examples the correct selector to enable the buttons with javascript is ".btn-group".
[doc] tweaked the appearance of the last item of the file listings
Fixes #10207: alert-dismissable example requires contextual class
per the docs - use <a> instead of <button>
add  role="button"
Compress PNG files losslessly.

Use zopfli with 1000 iterations, pngout /r with various blocksizes and deflopt.

assets/ico/apple-touch-icon-114-precomposed.png | Bin 2939 -> 2931 bytes
assets/ico/apple-touch-icon-144-precomposed.png | Bin 3614 -> 3549 bytes
assets/ico/apple-touch-icon-57-precomposed.png  | Bin 1577 -> 1573 bytes
assets/ico/favicon.png                          | Bin 889 -> 887 bytes

Total difference: -79 bytes.
Update Respond.js to v1.3.0.
Update html5shiv.js to v3.6.2.
Add bugs property to package.json.
Merge pull request #10210 from acmetech/master

Update the example for components/#btn-groups-justified to match the "Element-specific usage" callout
Merge pull request #10209 from clbn/master

Fixes #10207: alert-dismissable example requires contextual class
Merge pull request #10208 from javiereguiluz/patch-2

[doc] tweaked the appearance of the last item of the file listings
Merge pull request #10215 from XhmikosR/master

Various
Fixes #9991: Better docs for tabbable tabs and fade classes

* Adds full code snippets
* Adds snippet for `.fade`
* Adds callout for `.in` requirement on first fade-able tab
Merge branch 'master' of github.com:twbs/bootstrap
Fixes #10088: Simpler nested headings section in accessibility docs

* Headings, not headers
* Simplifies content compared to #10088 which adds quite a lot
* Uses proper heading elements (`h1` - `h6`) and not `header`
* Collects links at bottom instead of mid-paragraph
Merge pull request #10131 from andyen/master

correct enable selector for button usage in docs
Fixes #10082: document `.navbar-form`

* Adds new section to navbar docs with example
* Updates example classes for all collapsing navbars so their numbers
increment as you scroll
fixes #9901
Fixes #9928 and #9932: carousel example in IE10

* Use absolute positioning instead to remove navbar from flow of
document
* No more negative margin fu
* Flip around padding between container and navbar for proper display
in xs and sm viewports