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
Include .editorconfig

http://editorconfig.org/
replaced parametric .is() mixin with non-parametric .a() to simplify usage
Refined .editorconfig
Use* global rules with exceptions as needed
'root' repo end 'insert_final_newline = true'
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
Merge branch 'ntwb-editorconfig' into 3.0.0-wip
explicit callout in readme for building static assets; fixes #7632
shoutout to editorconfig in readme
Merge branch '3.0.0-wip' of github.com:twitter/bootstrap into 3.0.0-wip
'root' folder .editorconfig code guide updates
'less' folder .editorconfig code guide updates
'js' folder .editorconfig code guide updates
'docs' folder .editorconfig code guide updates
Merge pull request #7664 from ntwb/editorconfig-3.0.0-wip

Editor Config (.editorconfig) Code Guide Update
Include .editorconfig

http://editorconfig.org/