Change font to sans-serif

I also adjusted the line height slightly to give each menu item a bit more breathing space. Fixes #4

![f11f9afc-c31e-11e2-80c8-36f92e4763ac](https://f.cloud.github.com/assets/868834/562291/a16e5236-c4a5-11e2-9d8a-d447b6859054.png)