Add GPA to education sections

Hi, big fan of the theme. 

Dunno if you're interested, but I've made a small addition to show GPAs. Feel free to suggest any changes. 

I'm also planning to make a few more changes: 
- more date formatting (e.g. Education in *MMM, YYYY* format)
- links for publications 

Let me know if you're interested, no worries if not :)