kinda big changes:
- core methods updated to be used in a generator fashion with tornado.gen.Task
- moved util methods from response.py to utils.py
- created test_utils.py
- updated tests to use tornado.testing.gen_test
- BraspagRequest docstrings updated
Merge pull request #7 from luizalabs/ap-async-improvements

Generator-based interface for api calls and other random improvements