GPS-device handling functions

Files
file	gps-parser.h
	interface to GPS parser
file	gps-parser.c
	interface to GPS parser
file	nmea_hl.h
	interface to NMEA parser
file	nmea_hl.c
	NMEA parser implementation.
file	sirf3.h
	SiRF Binary Protocol handling.
file	sirf3.c
	dissect SiRF binary input message