New library for Frsky D-Receiver

The library uses a serial port to simulate Hub Port data.
you will need a level inverter between the Pixhawk and receiver (FUL from Frsky)
S-Port for Frsky X receiver is not implemented yet
Currently it implements
Barometer altitude (Alt)
Battery percentage remaining (Fuel)
Battery Voltage (VFAS)
APM Mode : T1
Nb of satellites and 3d lock : T2
GPS Alt : Galt
Heading : Hdg
GPS Coord 
GPS Speed