Add support for RS232 communication

[PixelsForBreakfast]

It would be amazing if there was an additional package to communicate with MRX receivers over RS232. That way the network control port wouldn't be blocked. I assume this could use pySerial, but I'm just a beginner with Python.

[rsnodgrass]

There is the package python-anthemav-serial that was being developed for Home Assistant integration for the RS232 supports Gen1 and Gen2 Anthem receivers/preamps.

It was pretty close to being completed, but I ran into some issues with deadlock during communication and have never had the spare time to sit down and debug what was going on. Too many other projects taking priority, but I hope later this year I get a chance to dig back into this....or hope someone will pick up the mantle and carry this over the finish line.