Piezo support

Fixes #92

This is based on the work by @deshawnbw and @pfiller https://gist.github.com/pfiller/5680471 but with correct nano timing using `nanotimer`, isn't the best resolution but the notes and the timing works like the example in: https://github.com/sparkfun/SIK-Guide-Code/blob/master/Circuit_11/Circuit_11.ino