audiotools.open does not recognize MP3 files in MPEG-2 or MPEG-2.5 format

Lines 1704 and 1712 of the script ```audiotools/__init__.py``` checks whether ```mpeg_id == 3``` (which means MPEG-1), while in fact ```mpeg_id == 2``` (MPEG-2) and ```mpeg_id == 0``` (MPEG-2.5) should also be accepted.