Test data handling
This branch contains a bunch of unit tests of the functions in data_handling.py. Also, some improvements to implementation of these functions (mostly, just adding assertions for the input arguments).
One minor problem I haven't managed to resolve: When using ffmpeg to extract a portion of a wav file, the selected portion does not seem to fit with the original signal. Perhaps it's just that ffmpeg rescales all signal values by an overall factor? @fsfrazao, could you please check? You are more familiar with ffmpeg than I am ...
The problem appears if you try to uncomment these two lines.