Sass/4.0 Alpha 1

A Sass port/rewrite of Animate.css. Features pending, but this is mostly a functionality—as opposed to design/animation—update. Some non-trivial changes include:

• Restructured files such that compiled CSS is in a new dist directory
• Added a mixin to allow easy inclusions of animations on any element
• Variables to adjust animation duration and the animation hook class name

Please add feedback to the open PR for the 4.0 release (#277).