0.18.0

• Dropped support of Python 2.7, 3.5, 3.6
• Fixed issue with type annotation for responses.activate decorator. See #468
• Removed internal _is_string and _ensure_str functions
• Removed internal _quote from test_responses.py
• Removed internal _matches attribute of RequestsMock object.
• Generated decorator wrapper now uses stdlib features instead of strings and exec
• Fix issue when Deprecation Warning was raised with default arguments
  in responses.add_callback due to match_querystring. See #464