Async methods

- Updated travis configuration
- Created requirements files
- Created Makefile to use nosetests with coverage
- Removed test with mock requests and responses -- which we'll eventually add back
- And, of course, changes to these methods to make them async: authorize, refund, void, capture, get_transaction_data, get_order_data, get_customer_data
- The above mentioned methods are now all class-based
- Docstrings of braspag/core.py updated
- Moved the mock data files to tests/data-unused, I think it's good to keep them in the tree so that we might reuse them if we can add mocked tests back in the near future
faz sentido descomentarmos ela depois. integrei sem ver esse comentário.