'make coverage' works w/ pytest-cov
Refactor code and tests

JsonApiMixin now has these (better documented) methods:
- render - Decides which wrap method to use, renders response
- wrap_default - Wrapper for 'good' responses
- wrap_error - Wraps in JSON API Error format, configured by params
- wrap_bad_request - Configure wrap_error for 400 Bad Requests
- wrap_generic_error - Configure wrap_error for other errors

Added "succeeded in creating resource" tests to test_list.py
Moved "failed to create resource" tests to test_errors.py
Render parser errors differently than field errors