Support for isochronous transfers

[alufers]

Hi!

I am in progress of creating a Rust application to display a feed from thermal cameras. They are UVC devices (with some nasty non standard features, which require an userspace driver), which use isochronous transfers to send the video.

It would be very nice to have a native Rust API for receiving isochronous data, since rusb doesn't wrap libusb for that and playing around with unsafe code, callbacks, and such is required.

PS: If you think this is out of scope to this project, feel free to close this issue. Many thanks for your library!