Allow to override GPS port speed in FlashTool
Use default 38400 GPS port speed if not defined other
Fixed wrong timings in ITG3200 driver

APM:Plane - fixed GPS port speed selection in FlashTool
Update readme to reflect new documentation
Fix ArduPlane compilation
Merge branch 'mpng_ArduPlane-2.75' of https://github.com/smurfy/ardupilot-mpng into mpng_ArduPlane-2.75