ENH: Add console visual

Ready for review/merge.

Closes #418.

Example output:

![screenshot from 2014-09-02 10 27 45](https://cloud.githubusercontent.com/assets/2365790/4122587/1b455534-32c6-11e4-9821-e0ca0e949bd6.png)

How about `font_scale`. It shouldn't be the same as what we call it in `Text` because it doesn't actually mean the same thing / have the same units at all. (It's actually a multiplicative scale factor that must be an integer, and the text lives in pixel units, so we don't want people thinking this has a simple relationship to point size.)