add company mode faces

No guarantees they work with all setups (I didn't test with all of the company-mode frontends), but here's a quick screenshot of most of the pseudo-tooltip:

![screen shot 2014-03-12 at 3 45 28 pm](https://f.cloud.github.com/assets/667901/2404199/5a80a602-aa38-11e3-9520-707f3fd3382a.png)

Tried to take as many cues from Light Table as possible.