Fix h3 text flowing into h2 text

As seen here: http://haacked.com/archive/2014/07/28/github-flow-aliases/ (search for GitHub Flow Aliases). Screenshot: http://cl.ly/image/0X2l1H2T2C2R

Also dropped the h3 font size a bit.
Merge pull request #135 from swilliams/patch-1

Fix h3 text flowing into h2 text