Added Velocity.JS support

[schme16]

I've added in a quick check for velocity.js (https://github.com/julianshapiro/velocity) as it is a lightweight drop-in replacement for the $.animate module.

Benefits of using Velocity.JS are that it minimizes layout trashing, it minimizes DOM thrashing and executes its steps inside of a window.requestAnimationFrame; it is also compatible back to IE6 delivering very high performance (better than css transitions in most cases).

I'd even recommend that you mention the benefits of including Velocity.JS in the readme.

Thanks for all the great work on this project over the years!