Stomp.py

* Merge patch from Nigel S, improving heartbeat accuracy (https://github.com/jasonrbriggs/stomp.py/pull/95)
* Merge various patches from Ville S (including):
* fixing receipt id generation (https://github.com/jasonrbriggs/stomp.py/pull/102)
* generate disconnect receipt ids (https://github.com/jasonrbriggs/stomp.py/pull/108)
* don't send unnecessary heartbeats (https://github.com/jasonrbriggs/stomp.py/pull/113)
* fix misdetection of heartbeats (https://github.com/jasonrbriggs/stomp.py/pull/120)
* Merge patch from Hugh P, adding SNI support (https://github.com/jasonrbriggs/stomp.py/pull/124)
* Fix for heartbeat calculation error (https://github.com/jasonrbriggs/stomp.py/pull/125)

* Minor tidy up (missed from prior release)

* Bug fix for header escaping (https://github.com/jasonrbriggs/stomp.py/issues/82)
* Merge patches from Ville S:
* heartbeats - set received timestamp on receipt and error too (https://github.com/jasonrbriggs/stomp.py/pull/79)
* test class name fixes (https://github.com/jasonrbriggs/stomp.py/pull/80)
* support \r\n\r\n preamble end on content-length search (https://github.com/jasonrbriggs/stomp.py/pull/81)
* on-demand logging message expansion (https://github.com/jasonrbriggs/stomp.py/pull/85)
* bump connect error logging level to warning (https://github.com/jasonrbriggs/stomp.py/pull/87)
* assign names to heartbeat and receiver threads (https://github.com/jasonrbriggs/stomp.py/pull/88)
* remove unused HeartbeatListener.connected (https://github.com/jasonrbriggs/stomp.py/pull/89)
* support for heartbeats on CLI (https://github.com/jasonrbriggs/stomp.py/pull/100)
* Merge patch from Mikael V:
* add header support in CLI (https://github.com/jasonrbriggs/stomp.py/pull/86)
* Bug fix for on_before_message error (https://github.com/jasonrbriggs/stomp.py/issues/99)

* 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)