Version 2.0

* Refactored code, making it much more DRY
* Better behaviour of just raising exception on a Bitstamp API error
* Backwards compatible (old lowercase class names still behave the same)
* Fixed tests
* Tests now use mock API calls
* Tox tests for easy cross-python testing
* Removed unsupported `bitinstant_reserves` call
* PEP8 tidy up, and docstrings galore