Initial code import

Rolling out direct mappings for the current REST-APIs. The test coverage is catching up but as it stands now it cover all the bases but doesn't test for corner cases. 

*Test suite is testing against the real service, this changes once the mocking code is complete.*

Some minimal documentation, currently Clearhaus::Client is fully documented along with some usage information in README. However, it'll certainly improve.

The existing implementation only covers authorization, capturing, voiding, refuding and tokenization of credit cards but doesn't expose any of the transaction listing APIs yet.
It's also a direct mirror of the REST-API that means, no wrappers. Methods expect the same params as do the REST counterparts and returns the parsed JSON.