Detect BPM from keystrokes

This plugin allows to detect the bpm of a song by listening to the user's keystrokes. The rationale is that sometimes the bpm is missing from the echonest database or it is simply plain wrong. To correct or simply get the bpm of `<song>`, start playing it, type `beet bpm <song>` and then press Enter three times to the rhythm. It works best if you wrap it in a script that gets the playing song, e.g. with mpc I do something like

`beet bpm $(mpc |head -1|tr -d "-")`

Credit: this feature was there in Banshee and I missed sorely since I moved away from it.