Fixes #468 - top-aligns superscript text.

Fixes #468 - top-aligns superscript text. Superscripted text was
aligned to the bottom of the surrounding text, this commit top aligns
it instead.

![screen shot 2014-10-06 at 7 04 43 pm](https://cloud.githubusercontent.com/assets/704760/4535059/504d9eba-4dad-11e4-9303-ab06dd420765.png)

![screen shot 2014-10-06 at 7 04 36 pm](https://cloud.githubusercontent.com/assets/704760/4535060/50515f5a-4dad-11e4-84c5-13ee49d6f85c.png)