GPS - adding some documentation.
Update serial port irq handlers so they avoid the % operator.
GPS - more documentaiton updates.
GPS - fix ubox maximum packet size comparisons.  Increase UBlox buffer
size to work with Glonass MSG-SVINFO packets.  Skip data from packets
that are too large to process without attempting to process a large
payout as packet data.  Ignore GPS presence check when enabling
passthrough mode so that it is possible to configure a GPS unit via the
FC without the GPS unit actually having communicated to the FC first.