this allows users to change the yaw gain in DCM

this adds local and remote radio noise levels

AP_MotorsMatrix - fixed stability patch issue in which it would not limit a motor's output unless an opposite motor had been defined.  This would only have affected Y6 frames.

AP_Motors - fixed last "shadowing" compiler warning caused by badly named parameter in auto_armed method.

AP_MotorsMatrix - fixed another compiler error regarding shadowing a variable.  Fixed by removing those  the angle and direction arrays which weren't even used

AP_MotorsHeli - fixed compiler warning re move_swash function declared with int parameters in .h file but actually using int16_t in .cpp file.  They're the same in arduino but perhaps the build checker is a little more strict that Arduino.

AP_Motors - fix compiler warning re shadowing a variable caused by badly named parameter in armed function.
Another compiler warning fixed in AP_MotorsMatrix.cpp caused by declaring "i" twice.

     1. it's step towards rearchitecting the current code base ahead of a move to RTOS.
     2. internally it uses a MatrixTable for the Quad, Octa, OctaQuad, Y6 frames.
     3. it implements the missing stability patch for Octa and OctaQuads (still missing for Y6)

Later check-ins will incorporate into the main ArduCopter code.

this allows us to put a serial port into non-blocking mode, so that
writes that don't fit in the transmit buffer are dropped. This will be
used in flight to prevent stray printf() calls from causing large time
delays in the code

when this is 1 (which is the default), we will get the declination
automatically via the AP_Declination library

when it is 0 we will use the value configured by the user

there was a comment saying this was too slow, but it actually costs
about 30 usec extra, which is trivial given the full auto declination
call costs 680 usec and its only called once per boot

AP_Declination: Update LUT based on the changes that I made in the LUT generation code. This LUT is the final version that has no truncation.

AP_Declination: Removed trailing zero deltas as they have no impact on the final value and only take up extra bytes.

AP_Declination: Updated compressed lookup value table. Located 9 more failure points due to truncation on the packed LUT.

AP_Declination: Found 7 of the 22 failure points and fixed them. The issue with those 7 was the way I originally packed the value array. The last delta values on some rows were getting truncated. The new number of failures is down to 15 - WIP.

AP_Declination: Updated test to run in 5 degree increments. Changed to only print failures and also print total pass vs total fail.

AP_Declination: The exception signs unpacking logic was incorrect. I was shifting a 1 value left y%8 which would have needed a the signs to be packed right to left. My packed signs byte was packed left to right (left most being the 0 position) so I needed to reverse the shifting.

AP_Declination: In order for the bitwise & operation to work, negative signs need to be represented by 1s instead of 0s. Changed so that negative signs are represented by a 1 in the packed signs array. Updated lookup logic to reflect this change.

AP_Declination: Added original array to test sketch. Added loop to validate new compressed array against original in 1 degree steps.

AP_Declination: Moved rows with large spikes in delta to their own unsigned exception rows. The signs are in a separate packed array.

AP_Declination: Implemented Delta Encoding and Run-Length Encoding. Added method to traverse the compressed array and return the lookup value based on the same lat_index/lon_index that was used before.

AP_Declination: Reduced the size of the lookup table to support -75 <-> 70 latitude range. This allows the datatype to remain int8_t.

when a user first connects with USB, and later switches to the
telemetry port without restarting we were getting zero for error_yaw
in the logs, as AHRS.get_error_yaw() was being called twice.

This ensures we give the last value after the counter is reset