added retina-image mixin
Added optional retina-filename
Added asset-pipeline support for rails
Replaced media-query with hidpi mixin
Removed image-height and width in favor of background-size variable
dont impose 2x naming for custom retina-filenames
Added double strand support to modular-scale function
Update readme.md

Fixed the broken logo image.
Add Placeholder support for firefox 19+
Add helper for prefixed backface-visibility property
Update linear-gradient mixin to spec
Extracted function to helper file. Make linear-gradient function work to spec. WIP
Bring radial-gradient function and mixin up to spec
Make background-shorthand mixin play well with the new gradient changes
Finished gradients updates to spec. Refactored helper functions to helpers directory
Fix bug in sass prefixer
Depreacted background-size mixin
Remove ms vendor prefix from keyframes mixin
Removed some prefixes and other cleanup
Merge branch 'pl-linear-gradient-spec'