BS3: Require .btn-default for all standard buttons

* Overhaul the form control sizing section to only show sizing via grid columns as parents, not as classes on inputs
* Restore the inline-form option
* Restore the bottom margin on form controls and make them block level instead of inline-block
* More misc docs cleanup for forms

* Instead of , use  for standard, gray button
* Improves ability to customize buttons by encouraging folks to not override .btn and thus overriding all button modifier classes
* Updates docs to reflect the change
* Reorganize buttons CSS

Updated URL for jekyll installation

fixed not working example code for modals

use @screen-small var in grid.less

Per comment by @nextgenthemes on/in cd06c5ba

Fix flickering on progress bar width update

Use @font-size-... variables instead of hardcoded font-size in px

Use padding instead of #push with box-sizing: border-box

Conflicts:
	docs/docs.html

Corrected typo in carousel.html

Fix input border flicker in Chrome

* 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

* 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

* 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