Add bleak backend to allow people without dongles to use pyomyo

[PerlinWarp]

The BLED112 dongle allows the Myo to work on any operating system as it acts as a COM port that forwards serial commands send to it over Bluetooth.

One reason why it's worth doing this is due to the poor cross platform BLE support, however bleak (Bluetooth Low Energy platform Agnostic Klient) may solve this and allow people without a dongle to use pyomyo.

This feature would also act as a stepping stone for makers of open source BLE EMGs to add support for their hardware to pyomyo.

Thankfully, Thalmic Labs released (most of the) the specification here.