* Drop Python 2.7 support, support Python 3.8
* Convert responses to raise `ProblemException` (955)
* Add error path to schema validation
* Do not sanitize body keys in OpenAPI 3 (1008)
* Date/time serialization (851)
* Forward options to AioHTTP app (885)
* Returning tuples supported in AioHTTP (849)
* Allow Swagger UI configuration options (948)
* Remove security parameter to pass query validation (470)
* Allow users to enable debug mode via environment variable