P25 "heuristiscs" module

Hi. For your consideration, I have completed an improvement on the important P25 getDibit method that translates an analog value into a dibit. I'm using a "heuristics" module that applies a simple Gaussian classifier over analog values. The error reduction on the two sample files from DSD-samples is quite noticeable, although there is still room for improvement on C4FM. More information is on the p25p1_heuristics.c file. I made an effort to document it, hope it's understandable.

Also included is error correction on the TDULC data. Error correction is now practically completed for P25. The error corrected data plays an important role in the afore mentioned heuristics module.

I've also included an estimate for the BER on P25. This is an initial approach, not sure how precise it is.

I'm sorry there are so many changes, I should have split them in separate commits. Now it's too late. Let me know of your comments.

Kind regards,

Ed