Use HIDAPI instead of PJRC for HID

We have been using a modified version of pjrc_rawhid to provide our HID API for a while. This
has caused a large number of crashes on OSX over the years. Swapping to HIDAPI

 https://github.com/signal11/hidapi

seems to fix this. I've tested with the bootloader and numerous connects and disconnects and so
far do not see any crashes from GCS. This needs testing on other operating systems, though.