Fix python module import warnings by not using dots

Previously imports were done using (for example)
imp.load_source('audio.mpeg.mpegaudioreader','audio/mpeg/mpegaudioreader.py').
This is incorrect and causes warnings, because audio and mpeg are not real
python modules (contain no code) and cannot be used. Separating the name using an underscore fixes the problem (we can't use / because it isn't a valid python identifier).