Bleak backend

[Jakeler]

Fixes #5

TODO:

• update readme
• clean up experiments, bluepy
• MTU parameter, default 20 byte like in Added UART service example. hbldh/bleak#480? Testing shows that indeed more than 20 causes crashes... Got improved with 4.2/5.0: https://interrupt.memfault.com/blog/ble-throughput-primer#bluetooth-low-energy-packet-structure
• Queue for ble notify -> write uart as well - improved packet loss
• Fix async execption handling, Traceback on Keyboardinterrupt, stop on disconnect

[Jakeler]

@AGlass0fMilk Could you please take a look and try this branch out? It works pretty well in my testing now, but I am unsure about the address type, is specifying it not required for BlueZ? Bleak uses the parameter only in the Windows dotnet backend as far as I can tell. Also let me know if you find any other bugs.

[AGlass0fMilk]

Hi @Jakeler I will look into this soon.

I've developed a BLE UART service for Mbed OS and made some integration tests using Bleak. Not sure if it's helpful now but you can find that work here:

https://github.com/EmbeddedPlanet/ep-oc-mcu/blob/0494973c512da087c11bd4a16dd5c4aa0dcd4cc2/features/FEATURE_BLE/experimental/TESTS/host_tests/ble_serial_test.py