0.20.0

• Deprecate responses.assert_all_requests_are_fired, responses.passthru_prefixes, responses.target
  since they are not actual properties of the class instance.
  Use responses.mock.assert_all_requests_are_fired,
  responses.mock.passthru_prefixes, responses.mock.target instead.
• Fixed the issue when reset() method was called in not stopped mock. See #511