Adding notes regarding the auxState variable.
Adding notes regarding rcOptions.
Formatting bitmask creation code for MSP status response.
BUGFIX - Cleanup failsafe system so it works correctly with Serial RX
systems and Parallel PWM/PPM systems.

Added setting for failsafe_max_usec.  Renamed failsafe_detect_threshold
to failsafe_min_usec.

Failsafe now detects when a PPM/PWM RX isn't sending ANY data out on
CH1-4.  See documentation notes regarding Graupner receivers in
Failsafe.md.

Documented failsafe system.
Improvement: Updated SUMD to support 16 channels.