AudioTransform: support resampling

* Use default interpolation (nothing to set).
* The default interpolation may be not optimized for some audio files:
need to set parameters used to resample (filter_size, phase_shift,
linear_interp, cutoff, etc...) before initialize the SWR context.
Merge pull request #90 from cchampet/dev_resample_audio

AudioTransform: support resampling