Big refactorization = 1.0.0

Added

• Use mypy to type codebase
• Request and Response tests
• Use @staticmethod where necessary

Changed

• Requests are now initialized with a dictionary of parameters(example on README)
• The code and message of a Response can now be accessed from response.code and response.message
• is_paid, is_refunded, is_canceled and is_authorized are now properties instead of methods

Fixed

• Correctly enforce abstract class