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
more nested labels component
replaced parametric .is() mixin with non-parametric .a() to simplify usage
Merge branch '3.0.0-wip' of https://github.com/twitter/bootstrap into 3.0.0-wip
Nuked local .a() mixins and simplified the nesting
Include .editorconfig

http://editorconfig.org/
Refined .editorconfig
Use* global rules with exceptions as needed
'root' repo end 'insert_final_newline = true'
Fixes #7661
explicit callout in readme for building static assets; fixes #7632
shoutout to editorconfig in readme
'root' folder .editorconfig code guide updates
'less' folder .editorconfig code guide updates
'js' folder .editorconfig code guide updates
'docs' folder .editorconfig code guide updates
- changed comments
- added hover and focus state for [href] color variations
Merge pull request #7641 from Fowowski/3.0.0-wip

more nested less rules - labels component
running make