[hist] fix potential memory leak
[utils] hist with size null fails
src/utils/: add const qualifiers
src/utils/hist.{c,h}: flow/fhig, now ilow/ihig
src/utils: switch to mono
src: update all headers to GPLv3
src/utils/scale.c: rename aubio_scale_set to aubio_scale_set_limits
src/mathutils.c and co: use 0.0, not 0.0f
rename vec_min and vec_min_elem to fvec_min and fvec_max_elem
rename vec_max and vec_max_elem to fvec_max fvec_max_elem
remove src/sample.h
src/: more moving and splitting