Use CSS to massively speed up animation

[The abstract is set out here](http://www.princeton.edu/~crmarsh/svg-performance/). I've not looked at the viability of this for C3 yet, but Kahn Academy have got major performance enhancement using this method. Leveraging CSS animation to get full use out of the browser GPU rendering and other optimisations, while working with SVG.

This is related to #172, but it is a specific idea, so I thought it should be looked at as a specific issue, and then either adopted or closed by itself.

I might add, that I have had some serious issues with C3 and performance, in data heavy apps. While this isn't a problem for drawing an individual chart on a page. Pages with multiple complex charts need all the help they can get.

Anyway, hopefully this suggestions is interesting and educational, even if it isn't practical for C3 :-D