Tweaking header sizes

This changes the headers sizes to span from 1.0 to 2.0 times the
size of the default font.

Here's what it looks like now:

![Screenshot 2013 03 21 10 53 41](https://f.cloud.github.com/assets/126398/286571/b4435c50-923f-11e2-814f-5fb6f2709f7d.png)