cleanups from pylint

changed load() signature
removed sr from stft
removed librosa.pad()
simplified melfb code
cleaning up beat code
fixed the hpss example
cleanups in experiments
linted output
more lint cleanups
cleanup hz_to_mel, mel_to_hz
cleanups in feature.py
numpy => np for readability
cleanups in beat.py
more linting in feature.py
massive refactor to the beat tracker
unit test for chromafb
chromafb passes
renamed n_filts => n_mels in melfb
fixed some docstrings