Python-engineio-v3

- Preserve exception in case it is lost before it is re-reaised ([commit](https://github.com/miguelgrinberg/python-engineio/commit/f0c2f5b444b57c7b80f262e90fcd608cd3af2deb))
- Added a port of the "latency" example from the official Javascript client ([commit](https://github.com/miguelgrinberg/python-engineio/commit/b976ff304e045aa375ec3f9f1f8f17483b2d1934))
- Allow application to provide a custom JSON encoder/decoder. ([commit](https://github.com/miguelgrinberg/python-engineio/commit/1e8fab676f83eab1b82778ab6dcd362609301d57))

- added b64 unit tests ([commit](https://github.com/miguelgrinberg/python-engineio/commit/c270acf1da2eb39e12049b86e58287aa9ce0dd71))
- Added b64 checks and encoding during initial connect [4](https://github.com/miguelgrinberg/python-engineio/issues/4) ([commit](https://github.com/miguelgrinberg/python-engineio/commit/ac90ed68668f617f347c08d0ea4c37ea56ac12c3)) (thanks **Myles Ringle**!)

- Improved handling of logging ([commit](https://github.com/miguelgrinberg/python-engineio/commit/142b9a66e1e29e5069696a8a2e9757bcb394b268))
- Make gevent websocket optional in example app ([commit](https://github.com/miguelgrinberg/python-engineio/commit/c6b1ae91e2e7c3ee8dfec3caf8a8dfa8c2800aa2))

- Make gevent thread arguments optional ([commit](https://github.com/miguelgrinberg/python-engineio/commit/3c4f10f266e694380104234294b9ccf2730c1263))

- Add WebSocket support for gevent (Idea derived from pull request [1](https://github.com/miguelgrinberg/python-engineio/issues/1) by drdaeman) ([commit](https://github.com/miguelgrinberg/python-engineio/commit/96dc09b0119a816aada9ad787344ccc912608d55))
- Made parsing of HTTP connection header more robust ([commit](https://github.com/miguelgrinberg/python-engineio/commit/f1ce5e0f5b904e44d587d6dc5aab44800f73cf40))
- Refactored the three async modes as separate modules for greater flexibility (Idea derived from pull request [1](https://github.com/miguelgrinberg/python-engineio/issues/1) by drdaeman) ([commit](https://github.com/miguelgrinberg/python-engineio/commit/a85ac4c97e5a5e0d2ecdfd273673b479c0b6c7ff))
- Fix executable bit on several files ([commit](https://github.com/miguelgrinberg/python-engineio/commit/47bc67efc86c3043f4b3c786eea9776a04222e04))

- Correct handling of CORS origin header ([commit](https://github.com/miguelgrinberg/python-engineio/commit/394a87877e49424461a2c4053e9ce8c216c093b8))
- minor improvements to the example application ([commit](https://github.com/miguelgrinberg/python-engineio/commit/c02a58795bb133f4eb80e7f4d0c64c3a9281c7c3))
- documentation improvements ([commit](https://github.com/miguelgrinberg/python-engineio/commit/f9eaa604d3025aa88a075ab13908ad27ca2b32f1))