Django-oscar-cch

- Add support for calculating taxes on shipping charges.

- Handle case when CCH returns an error code during order placement.

- Remove StatsD counters and timers.

- Add ability to pass in a ``pybreaker.CircuitBreaker`` instance into the ``CCHTaxCalculator`` constructor. This allows implementing the CircuitBreaker pattern, thus enabling better handling of CCH web service outages. See the `pybreaker <https://github.com/danielfm/pybreaker>`_ documentation for implementation details.

- Add support for django-oscar 2.x.
- Drop support for django-oscar 1.x.