standalone programs which take an audio file as argument

some of these rely on libraries which are not MIT-compatible

* [audio-bpm.py](./audio-bpm.py) detects the BPM of music using the BeatRoot Vamp Plugin; imports GPL2
* [audio-key.py](./audio-key.py) detects the melodic key of music using the Mixxx fork of keyfinder; imports GPL3