Optimisation of Fixed Point atan2_approx

[Thanduel]

The algorithm currently used in the atan2_aprox has a very large error term for its performance.

To improve it I suggest the use of a CORDIC algorithm. A CORDIC algorithm calculates the angle by working out, through a binary search of precomputed values, what angle rotation would reduce the original angle to zero. All the numerical operations are done in power of 2 operations.

This should at least double the performance for a slightly smaller error (3.576deg vs 4.5deg) term or give slightly faster performance for a sub 0.5 deg error term.