Altering `Piezo` to be able to take song notes without beats (default 1), notes as frequencies, or even a single note not in an array. Tests accordingly.
Making the `tempo` attribute of `tune` on `Piezo.play` be a BPM tempo instead of ms indication. Tested.
Added callback parameter to `Piezo.play`.
Merge pull request #3 from lyzadanger/piezo-tempo-api

Piezo Tempo and API Changes