Feature/twinx

Support for multiple axes.

![screen shot 2014-09-03 at 11 06 44 am](https://cloud.githubusercontent.com/assets/1078448/4137131/533f729e-3384-11e4-8d3d-b61e8f2a742b.png)
At first this explanation made me more confused, but now I see that `{x,y}_range_name` is implemented in other renderers as well. So, what's the reason not to use, say, `Instance(Renderer)` instead?