Add support for audio over USB

[v3rm0n]

• Add possibility to choose an audio output device
• Use async libusb API so that it works better with audio

[laamaa]

Thanks! :) Could you please update the regular Makefile too to pick up the new files and add stdint.h to the ringbuffer's includes?

[laamaa]

(It might be a good idea to mention the possibility of specifying the device name in README.md too)

[v3rm0n]

Does it work now?

[laamaa]

Yep, thank you! :)