[Tetrapol-kit] Viterbi algorithm

Hi ! Here is a first version of an error-correction using a Viterbi algorithm, which correct more errors than the current frame_fix_errs(). I put a limit on the errors (if there are too many errors, we suppose that the frame is broken, otherwise too many "random packets" are considered valid, since the CRC control has only 3 or 5 bits).