Update Voice.py

* optimized freq_search, making it faster (and less accurate, but still good to around 1Hz)
* tested by writing "freq" which finds base-freq of each small segment of record; takes around 6processing-seconds/record-sec for segment-durations around 0.02 seconds; note that although this processing speed turns out to vary with segment-duration, it does so slowly because twice the number of segments => each segment half as long => half as long to process each segment, and they cancel.
--- OUTCOME of TEST: got mixed 470/235 frequencies (true base was 235) but perhaps second harmonic strong. => TODO: don't use just strength as criterion in freq_search and freq; also use gcd relation to other freq.s, and history.