Remove dependency on sox to split/trim wave files

[shuttle1987]

If desired we could implement a pure python standard library only version of functions like trim_wav_ms by using the wave module https://docs.python.org/3/library/wave.html

[oadams]

That would be good but I agree with your labelling this low-priority. Calling sox for now is fine.

[shuttle1987]

I guess one thing is that sox may be a whole lot faster depending on how the standard library wave module is implemented. This might be a good first issue for someone to contribute?

[oadams]

Sure, since it's pretty orthogonal to everything else.

[shuttle1987]

It seems as though Kaldi needs sox anyway

[shuttle1987]

I think this might be a situation where it makes sense to use this standard library function as a fallback only if sox is not available.