feature($github): Add issues support

add support for github issues (as far as it exists in github.js at the moment)
feat($github): Add listPulls

add support for listPulls. This is a clone of https://github.com/PascalPrecht/angular-github-adapter/pull/7 but with tests and should include the travis fix mentioned in that PR, since that one seems dead.
feature($github): Add getPull

Along the same lines as the listPulls PR, adding repot.getPull(number)
to get an individual pull request.
Merge pull request #12 from m0dd3r/list_pulls

feat($github): Add listPulls
Merge pull request #14 from m0dd3r/get_pull
Merge pull request #11 from m0dd3r/add_issues

feature($github): Add issues support