Avoid hardcoding sampling rate

[Ashoat]

Instead of hardcoding a specific sampling rate, we should pull the sampling rate from the audio device we're using. #14 was a first attempt at this, but I want to fix it up to avoid setting the sampling rate to a static variable

[revbucket]

Commenting so I can get notified about this when progress is being made. Pending the resolution of the
madmom timing issues, it's a nearly trivial fix to ensure that the pyAudio/portAudio stream is opened under the desired sampling rate.

[Ashoat]

You can actually subscribe to updates on an issue by pressing the “Subscribe” button. As for Madmom sampling rate - unless there is a bug in how Madmom works, I don’t think there’s any reason that it needs to have the same sampling rate as Spectrum.