Update gps.h

Add hdop information in order to display GPS quality signal in telemetry
Update gps.c

Compute GPS quality signal
Merge branch 'pulsar256-master'
Merge pull request #93 from airmamaf/patch-2

Add Horizontal Dilution Of Precision to telemetry (1/2)
Merge pull request #92 from airmamaf/patch-1

Add Horizontal Dilution Of Precision to telemetry (2/2)
Minor documentation amends

Post proofing amends