Next Generation Aout Euro/ MI Yarns port

[Altitude]

I've built a bit of experience with this and that euro module in the last year or so and been working on my own Aout in parallel and found it's pretty unsuitable in it's present state.  Namely:

The bipolar circuit is referenced to the power rails and in a full euro cab, that is a VERY bad idea, massive noise ingress is the result making it useavle.  Removing that part of the circuit brings it back to very decent levels but 0-10V isnt terribly useful in euro.  Also, scaling the DAC outputs with a trimmer is a bit crude, per volt adjustments would be MUCH better (like in Ornament_crime or Yarns).

My idea is to keep the MAX525s since they are available and decent parts and serial addressed but switch the analog output stage to that of Yarns or O_C (-3 to 7V or -3 to 6V outputs respectively) and port over the code for the calibration of those devices (whichever is easier).  The hardware side is covered but I really need someone who can code to deal with that end of it.  O_C is teensy 3.2 base but Yarns is STMF405 which should be very close to the current core code base..

I'll provide hardware to work with for any takers