Documentation needs updating

[soundspotter]

The tutorials need some updating. Keyword arguments for features are now expanded python dicts, using the **kwargs syntax.

E.g. the following feature instances are equivalent:
LinearFrequencySpectrum(audio_dir+'fastcar.wav', nfft=2048, wfft=1024, nhop=512)
LinearFrequencySpectrum(audio_dir+'fastcar.wav', **{'nfft':2048, 'wfft':1024,'nhop':512})