Make social links more social

Instead of just a link to our GitHub repo, we can have a button that encourages people to star.  Instead of a link to our twitter feed, we can encourage people to tweet.  For people that g+, we have a link that encourages them to g+1.

Without these changes:
![before](https://f.cloud.github.com/assets/41094/272433/78f6f096-9003-11e2-83cd-ee81829f0ec1.png)

With these changes:
![after](https://f.cloud.github.com/assets/41094/272435/7fdfdc6a-9003-11e2-8798-6225210b55e5.png)