Add unit tests for GitHubRepository class
Rename all unit tests classes to use py.test instead of nosetests
Add testing functionalities to setup.py

- Remove dev_requirements
- Tests should now be run using "python setup.py test"
- Add requirements to test_requires
Refactor all unit tests to using pytest

- Define MoxTestBase using setup_method() and teardown_method()
- Use assert ... across the board
- Use pytest parametrization as much as possible
- Use capsys when appropriate
Add changes to .travis.yml
Rename integration tests to be recognized by pytest
Refactor all integration tests to using pytest