Swanky new demo page

ExpandingTextareas' `pre` element is a really elegant solution to the expanding problem.  I wanted to demonstrate how this works with a nice 3D demo.  (It looks best in Chrome!)

[![screen shot 2014-04-18 at 19 05 18](https://cloud.githubusercontent.com/assets/3473798/2744323/088536d4-c724-11e3-8c1e-f5c4b4c856ea.png)][1]

**Checkout a [live demo][1]**

I appreciate that this PR isn't really an essential part of the plugin, but I thought I'd send it your way in case you were interested. Feedback and criticism welcome!

[1]: http://iamdanfox.github.io/ExpandingTextareas/