Fix flickering on progress bar width update

Issue visible on lastest version of Chrome Browser (if you update progress bar width from 100% to 0%) -> flickering appears

Fixed with addition of .backface-visibility(hidden) mixins
update docs
Redo the getting started section to mention BootstrapCDN
Use @font-size-... variables instead of hardcoded font-size in px
Corrected typo in carousel.html

Changed text from "First featurette headling" to "First featurette heading" in the first `h2.featurette-heading` tag.
Use padding instead of #push with box-sizing: border-box
Fix input border flicker in Chrome from @garoevans, closes #7689
add customizer link to docs homepage
Cleanup .navbar-form styles

* Nuke the commented out navbar forms code that's not currently needed
* Add a few more examples to the .navbar-form docs section
* Remove (for now at least) top padding on checkbox and radios
delete lingering navbar dividers code since we nuked that awhile back
Improve buttons in navbars

* Add top margin, calculated by subtracting height of an input from height of a navbar, and dividing by two
* Uses the same method as .navbar-form
* To use, add .navbar-btn to any button outside a form element
* Also add section to docs detailing buttons in navbars, and add more ids for the other unlinked and unmentioned sections in the side nav
More navbar CSS and docs cleanup

* Rearrange sections
* Add code snippets for text and links in navbars
* Add .navbar-link back in
* Add mention of .navbar-text, but it still needs to be re-implemented
* Update nav to reflect new order
run make on previous commits
Merge pull request #7770 from holic/3.0.0-input-border-transition

Fix input border flicker in Chrome
Merge pull request #7762 from sethlilly/3.0.0-wip

Corrected typo in carousel.html
Add cursor: pointer; to .checkbox and .radio and their inline counterparts
Merge branch '3.0.0-wip' of github.com:twitter/bootstrap into 3.0.0-wip
Merge branch 'bs3_cdn_docs_mention' into 3.0.0-wip

Conflicts:
	docs/docs.html
Merge pull request #7769 from holic/3.0.0-sticky-footer

Use padding instead of #push with box-sizing: border-box
remove .fade from static modal example, but include in code snippet