Add font definitions again

Apparently you need to define every style
(normal, italic, bold, bold_italic) or else
it'll bug out when calling an undefined style
rather than using a fallback.

You can find OpenSans here, as I will not be including it in this repo:
http://www.google.com/fonts/specimen/Open+Sans
(click through for download page)
Or here:
http://www.fontsquirrel.com/fonts/open-sans