Proxima Nova disallowed, switch to Source Sans Pro

Adobe typekit was broken, specifically because we were trying to use the script generated for tom.preston-werner.com's account (CEO of github)

https://typekit.com/colophons/jpd0pfm <- link if you click on the "powered by typekit" button on bottom right corner of the blog

I replaced it with google web fonts and Source Sans Pro, which is a very similar account.

Inconsolata was added as well, since that was what was requested, and its very similar to Consolas, which is what you'll see if you're on windows (Inconsolata is a free font though).