Start working on serial in C

Implemented.  Start testing.
Merge print and mavlink branches.
USB Serial
Merge branch '31-usb' into 36-print-mav

Conflicts:
	Makefile
	RX.h
	TX.h
	dialog.h
	hardware.h
	mavlink.h
	openLRSng.ino
	serial.c
	serial.h
Dosify for merge
Merge branch '36-print-mav' into 37-merge

Conflicts:
	Makefile
	RX.h
	TX.h
	mavlink.h
	openLRSng.c
	serial.c
	serial.h
Cleanup