Tri-Copter implementation

[dmyers7]

Thank you for creating this repository! I see the main example is for a Quadcopter, I'm hoping to morph this into some additional mixing code to utilize 3 motors and a servo for use on a trip-copter setup. Clearly it is not as simple as mapping yaw into the servo instead of motor differential, as I assume there is coupling into roll and pitch that needs to be compensated for, but looking at giving it a go. Anyone already have experience / code to accomplish this utilizing madflight? if not I may eventually fork this to develop it.