Move examples out of the main repo to twbs/bootstrap-examples

While examples are phenomenally useful and awesome for folks getting
started with Bootstrap, they don't really shine as well being buried in
the main docs. Moreover, having anything that's not core HTML, CSS, JS,
or documentation in the main repo seems to just get in the way.
Therefore, examples gets its own repo.

Specifically, we're doing the following:

* Deletes all example screenshots
* Deletes example layout
* Deletes example files
* Updates Getting Started docs to include only the template and a link
to the new examples project

All the examples and their history will be preserved in the switch.
Docs: create new callout classes
Update mixins.less

Add a the function .make-small-column. See also http://stackoverflow.com/a/17308128/1596547
Adjust info callout, add callouts to docs

* Adjust the background-color of bs-callout-info to match danger and
warning in tone
* Convert all the callouts
* Change some callouts to info/warning
* Add new callout
Tooltip: apply position class before positioning
Remove unneeded prefixes

Per caniuse, prefixes for transitions and transforms can be reduced to just `-webkit` and `-ms`. http://caniuse.com/#search=transform
http://caniuse.com/#search=transition
Carousel no longer dependent on glyphicons

Used laquo/raquo for control buttons
Updated docs
rename .retina-image => .img-retina
Update forms.less

All variables should be set in variables.less?
rm .control-group from docs since it's no longer in the LESS
Merge pull request #8455 from cvrebert/control-group-dead

rm .control-group from docs since it's no longer in the LESS
Merge pull request #8454 from bassjobsen/patch-2

Update forms.less
Merge pull request #8453 from cvrebert/retina-rename

rename .retina-image => .img-retina
Update customizer

Add all the new things to customizer:
* `@headings-font-family`
* `@container-*`
* darker `@btn-default-bg`
Merge pull request #8478 from juthilo/3.0.0-customizer

Update customizer
fix broken scrollspy example
Merge branch '3.0.0-wip' of github.com:twitter/bootstrap into 3.0.0-wip
Add missing backtick in comment
remove webkit-overflow-scrolling from modal for now /cc #8495
Merge pull request #8498 from cvrebert/patch-1

Add missing backtick in comment