**Changes:**
* DNS parsing has been re-written which should be more stable
and handle more use cases
* TCP keep-alive has been added to more platforms, FreeBSD being one of them
* Player management has been totally re-written for MRP, so hopefully
play state should be more accurate now
* A delay has been added to turn\_off (MRP), so it should work again
* A heartbeat loop has been added that sends a "heartbeat" to the device
every 30s to detect connection problems
* Protobuf definitions have been further lifted to match later tvOS versions
**Notes:**
* Fixed a bug where Playing instancess were not immutable
* Push updates are only issued when something in the Playing instance changed.
Previously, unrelated changes to the device could trigger push updates with
the same content in Playing.
**All changes:**
0994733 build(deps-dev): bump tox from 3.21.2 to 3.21.3 (946)
8e0fc01 mrp: Add some protobuf messages for volume (947)
5752ae3 mrp: Fix handling of active client (944)
7e3bcf5 if: Convert Playing to data class (943)
2b8fb74 build(deps): bump pytest from 6.2.1 to 6.2.2
607d78c build(deps): bump mypy from 0.790 to 0.800
a77c453 build(deps-dev): bump tox from 3.21.1 to 3.21.2
393efbd build(deps): bump pytest-cov from 2.11.0 to 2.11.1
6bb284f build(deps): bump pytest-cov from 2.10.1 to 2.11.0
3c488b2 build(deps): bump deepdiff from 5.2.1 to 5.2.2
cc41f33 mrp: Add support for heartbeats (925)
aec7362 mrp: Add support for heartbeats (926)
9af7609 dns: Use UTF-8 for names, and (attempt) to handle dots in names (927)
b527506 build(deps-dev): bump tox from 3.21.0 to 3.21.1
fdf843f mrp: Support default supported commands (924)
f0f7eaf mrp: Add delay in turn_off between commands (923)
df56149 mrp: Add fields to UpdateOutputDevice (921)
280de0f Do not post duplicate push updates (920)
f9f7238 build(deps-dev): bump tox from 3.20.1 to 3.21.0
aed9028 mrp: Fix a few playback state edge cases (916)
e176ce7 mrp: Improve client and player handling (915)
3ca2b0f support: Add new tvOS versions to list (913)
ccfa5eb mrp: Major updates to protobuf messages (912)
3eb9d3a Improve DNS message parsing for mDNS (899)
c524244 build(deps): bump deepdiff from 5.0.2 to 5.2.1
87a159e build(deps): bump typed-ast from 1.4.1 to 1.4.2
e61fb47 Slightly refine protobuf and srptools base requirements (902)
b2e80b3 net: Use TCP keepalive on more platforms (897)
03e4438 build(deps): bump codecov from 2.1.10 to 2.1.11
f3dd0af build(deps): bump pytest from 6.2.0 to 6.2.1
5f3383b build(deps): bump pytest-xdist from 2.1.0 to 2.2.0
5ccb23f build(deps): bump pytest from 6.1.2 to 6.2.0