Add support for Enttec DMX USB Pro Mk2

[OliRead]

Add support for Enttec USB DMX Pro Mk2, documentation for required functionality can be found at: https://dol2kh495zr52.cloudfront.net/pdf/misc/dmx_usb_pro_api_spec.pdf

[OliRead]

I have now received the DMX USB Pro Mk2 device and have started looking at how it will connect to the library. I need to purchase a 5 pin DMX to 3 pin XLR adapter for my lighting rig to fully test this but I'm hoping to release within 4 weeks

[OliRead]

Another quick update, XLR adapters have arrived and I'll be starting work on this tomorrow.

[OliRead]

Partially resolved in branch: add-support-for-enttec-dmx-usb-pro-mk2
A full release will come soon.

see commit d70d641 for current work