arm_cmplx_mag_q15 reworked to be more accurate but less efficient.
New function arm_cmplx_mag_fast_q15 introduced to retain previous
(less accurate) but faster behavior.
Improvement to Python wrapper to support the new functions.
This first version is not very accurate due to problems with the log.
A coming commit will improve the log accuracy.
Issues #1305 and #1304 also corrected as part of this commit.
Christophe Favergeon