Python-socketio

- documentation updates ([commit](https://github.com/miguelgrinberg/python-socketio/commit/e56ff807f4faabb4e7ef339fda79de5b8a201b26))
- do not allow callbacks outside of a server context ([commit](https://github.com/miguelgrinberg/python-socketio/commit/6ae89688d72ec7f570a0b04a1bbf0483865bb5b5))
- message queue documentation ([commit](https://github.com/miguelgrinberg/python-socketio/commit/8ee4cf7e7557aeb02079c8402029eec5b68c79b6))
- pubsub unit tests ([commit](https://github.com/miguelgrinberg/python-socketio/commit/71142aa2db1434ab799edebeaa97020c6ec21089))
- README typo fix Important typo fix in README example code. ([commit](https://github.com/miguelgrinberg/python-socketio/commit/71e99d9a6b0804942bb9e507b3ce984143bee3ba)) (thanks **Davis Miculis**!)
- Support for callbacks across servers ([commit](https://github.com/miguelgrinberg/python-socketio/commit/63f5ed3429f96afd8f3a7cd82f281c2e5db93de1))
- initial implementation of inter-process communication ([commit](https://github.com/miguelgrinberg/python-socketio/commit/47620bbebd92a1b388df72a88c0ca35cdb530073))

- Correctly handle payloads that are empty lists or dictionaries [5](https://github.com/miguelgrinberg/python-socketio/issues/5) ([commit](https://github.com/miguelgrinberg/python-socketio/commit/a72f2dfb052d1f60a81edf1bb783c7aa4562f124))
- Added python 3.5 to the tox build ([commit](https://github.com/miguelgrinberg/python-socketio/commit/3cb904cfd83f7407b2e6317b349bea925c7333a4))

- support packets with empty payload given as an integer ([commit](https://github.com/miguelgrinberg/python-socketio/commit/d31d167c78203732c74a97f5a98788462231e01f))

- fixed regression introduced in latest release with ack ids ([commit](https://github.com/miguelgrinberg/python-socketio/commit/4a4ba41d0c7c6c5547fc73065ab2279ca7fce76b))