Many GPS radios provide both a 1-PPS and time of day information via
NMEA sentences. This patch introduces a ts2phc master that decodes
the "recommended minimum data" sentence, RMC, which provides UTC time
and a validity flag. Together with the file based leap second table,
this sentence provides adequate time of day for determining the time
of the PPS edge.
Signed-off-by: Richard Cochran <richardcochran@gmail.com>