Stomp-py

* Merge patches from Pavel S:
* support mixed string and bytes as input (https://github.com/jasonrbriggs/stomp.py/pull/66)
* toggle sending of `content-length` header (https://github.com/jasonrbriggs/stomp.py/pull/67)
* Minor logging change
* Various documentation updates
* Merge code improvement patches from Ville S:
* use time.monotonic for timekeeping where available (https://github.com/jasonrbriggs/stomp.py/pull/74)
* define gcd compat only where needed (https://github.com/jasonrbriggs/stomp.py/pull/75)
* handle locking with "with" (https://github.com/jasonrbriggs/stomp.py/pull/76)
* misc small improvements (https://github.com/jasonrbriggs/stomp.py/pull/77)
* Merge patch from nigelsim to improve heartbeat handling for ActiveMQ:
* heartbeat flexibility to support ActiveMQ (https://github.com/jasonrbriggs/stomp.py/pull/78)

* Fix missing import (https://github.com/jasonrbriggs/stomp.py/issues/61)
* Code tidy up

* Merge patches from Ville S:
* use constants more (https://github.com/jasonrbriggs/stomp.py/pull/56)
* do not send headers with None values (https://github.com/jasonrbriggs/stomp.py/pull/57)
* Update source to tidy up documentation
* Add sphinx generated documentation
* Fix keepalive bug (https://github.com/jasonrbriggs/stomp.py/issues/60)

* Generic exception catch on heartbeat send
* Fix timeout (https://github.com/jasonrbriggs/stomp.py/issues/55)

* Remove incorrect \r escaping from 1.1 protocol
* Merge patch from Ville S:
* don't ship *.pyc (https://github.com/jasonrbriggs/stomp.py/pull/52)

* Add --ssl option to command line tool
* Disable CTRL-C in command line tool (when in interactive mode)
* Add shutdown message to cli