Bump the copyright year
Update CONTRIBUTING.rst

Add not about how to use the issue tracker
Expose the stargazers count for repositories

I'm now using repo._json_data['stargazers_count'], which is a hack.
Making it part of the proper API.
Merge pull request #193 from seveas/stargazers

Expose the stargazers count for repositories
Merge branch 'develop' of github.com:sigmavirus24/github3.py into develop