Python-engineio-v3

- fix documentation builds ([commit](https://github.com/miguelgrinberg/python-engineio/commit/107b751f16aafff5842894a6eff26eb6f784ea5c))
- Suppress "socket is closed" stack trace from logs [57](https://github.com/miguelgrinberg/python-engineio/issues/57) ([commit](https://github.com/miguelgrinberg/python-engineio/commit/7dfc60e91f076e4a70a771cf98f16ceaa3de077c))
- Reraise exceptions in a Py2/Py3 compatible way [58](https://github.com/miguelgrinberg/python-engineio/issues/58) ([commit](https://github.com/miguelgrinberg/python-engineio/commit/4a3320051aac532918b1e0448aad8cc8da615697))

- Fixed poll() method to always empty the queue [589](https://github.com/miguelgrinberg/Flask-SocketIO/issues/589) ([commit](https://github.com/miguelgrinberg/python-engineio/commit/e8e665b1737987a2b7c59cd6a96464842b864bad))

- remove double-utf8 encoding hack this hack that made some incorrectly encoded packets sent by the JS socket.io 1.x clients does not always work, and is not needed anymore since the 2.x clients have been fixed. ([commit](https://github.com/miguelgrinberg/python-engineio/commit/83d2277de727e418b0abd1b1115a15307835d582))
- Documented protocol defaults ([commit](https://github.com/miguelgrinberg/python-engineio/commit/e6985ccfa9001aebfa31007dcae70989f2a4792f))

- cleaner disconnecting of polling clients ([commit](https://github.com/miguelgrinberg/python-engineio/commit/8d541fa2eb2f464b659baf0904de37567120f4bc))
- Support async_handlers option for the asyncio server [95](https://github.com/miguelgrinberg/python-socketio/issues/95) ([commit](https://github.com/miguelgrinberg/python-engineio/commit/6609416d2a0c7b8e750dcf1634f8a4218f5360e9))

- Tolerate errors when cleaning up a task cancellation [110](https://github.com/miguelgrinberg/python-engineio/issues/110) ([commit](https://github.com/miguelgrinberg/python-engineio/commit/a504e6b53fbb963c817755e57164ba07621aa253))

- better error handling strategy [49](https://github.com/miguelgrinberg/python-engineio/issues/49) (again and hopefully better) ([commit](https://github.com/miguelgrinberg/python-engineio/commit/8cc004a4a8014924dd822ca14ecabdad4e858c0d))
- Reraise app exceptions with the correct traceback [49](https://github.com/miguelgrinberg/python-engineio/issues/49) ([commit](https://github.com/miguelgrinberg/python-engineio/commit/66b8f5d63d9583ea1cbd3bb0eb9b4db8f8047ce5))