RawHID support

It would be great to get the HID device capabilities extended by raw HID. Raw HID is a great way for very robust bidirectional communication with a USB host application.
This is implemented for Teensy and by NicoHood for older AVR Arduinos. It would be incredibly helpful to have this functionality implemented for the SAMD line as well.

For some extended reasonsing as to why this is an important feature. See my post in the CircuitPython HID repo: https://github.com/adafruit/Adafruit_CircuitPython_HID/issues/25#issuecomment-409014365

https://github.com/PaulStoffregen/cores/tree/master/usb_rawhid
https://github.com/NicoHood/HID/tree/master/src/SingleReport

Start by reading the SAMD core and the referenced usb_rawhid implementation in Paul Stoffregen's cores repository, then compare NicoHood's SingleReport implementation for older AVR Arduinos. Define the SAMD-specific scope and verify that raw HID supports robust bidirectional communication with a USB host application.

Written by the indexing model from the issue text.