T60 gives strange results with multichannel files #261

I noticed when I call acoustics.room.t60_impulse(rir_path, bands) that if rir_path is a multi-channel file, then the T60 is not what I expect at all. For example, when pass a 30-channel file with a 0.5 sec IR, the T60 is 207.79.

Maybe there should be an error thrown if a multichannel file is passed, or a warning and only measure the 1st channel?

I have not tried with other similar room functions, i.e. c50_from_file or c80_from_file