Fix Github Issue count

Even though GitHub doesn't consider issues and PRs to be the same thing any more, their API still does. This change updates the ajax call to fetch 100 "PRissues" from the API, remove the PRs, and display a count. If that count is fifty or more, chances are good that there are more issues in subsequent pages, so just display "50+" and call it day.

![screen shot 2014-11-04 at 3 49 50 pm](https://cloud.githubusercontent.com/assets/2289/4910278/60971404-647d-11e4-83a7-885685d882a2.png)

cc @seldo 

Fixes #214