Select which CH341 to use

[mk-pmb]

As mentioned in the libusb docs, libusb_open_device_with_vid_pid is nice for simple tests but too limited for serious use. Is any somewhat experienced C programmer reading who could upgrade our detection so I can select a specific CH341A via bus number and device number? I might try and implement it myself but it's a long time since I've last dealt with C, so not sure if my attempt will be as helpful as I'd hope. (Usually I use python for USB stuff.)