Fix compile errors
ArduPPM: throttle failsafe is now triggered on single channel loss but recovery from the throttle low is possible
ArduPPM: added a define for throttle low fail-safe indication
ArduPPM: changes for throttle low indication and also recovery after a throttle low indication are now set with defines
ArduPPM: latest changes are now disabled by default, throttle low triggering by single channel errors and also recovering from a throttle low event can be enabled with defines
Merge pull request #6 from julianoes/ppm_encoder_fixes

ArduPPM

Two new defines added:

_THROTTLE_LOW_FAILSAFE_INDICATION: Throttle low indication and thus APM fail-safe triggering when a single channel error is detected.

_THROTTLE_LOW_RECOVERY_POSSIBLE: Throttle low is reset when a disconnected channel comes back and full control regained.