doc/*.cfg: update to doxygen 1.8.5
src/pitch/pitchyinfft.h: improve documentation
tests/src/pitch/test-pitchspecacf.c: add simple test
src/aubio.h: add pitchspecacf, remove from python/lib/generator
src/tempo/beattracking.h: improve documentation
src/utils/hist.{c,h}: flow/fhig, now ilow/ihig