This minor revision includes mainly bug fixes, but there are a few new features as well.
Optimize the following method :
* Spectrogram
* linear_spectrogram
* mel_spectrogram
* bark_spectrogram
* erb_spectrogram
* cqt
* vqt
* Cepstral coefficients
* mfcc
* bfcc
* gtcc
* cqcc
Adjustment of some parameter default values.