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)
The user can supply extra (arbitrarily) named ranges to associate with the plot. Then they can configure glyphs or guides to use the other ranges (by name) instead of the default ranges.