Host sprite.js on cdnJS

[talklittle]

Hi, I love the work you have been doing on sprite.js. Excellent library. I think it's a good time to start thinking about some free CDN hosting as the library matures.

If you look at https://github.com/cdnjs/cdnjs they have extremely simple instructions for submitting your library to be hosted. It requires constructing a small JSON description file and submitting a pull request.