Ported it to c without arduino dependencies. Switched from printf to a simple uart library.

Hey,
I just ported the driver to plain C without arduino dependencies (only avr-libc) for a project I'm working on where I do not use arduino. I also removed any printf references because I really do not like printf on AVRs ;)
Upside: It should be smaller and faster.
Downside: It is probably not arduino-compatible anymore, and it now needs a existing uart library. Also, it is not able anymore to control more than one chip (though that would be an easy fix).
Perhaps pull this into a separate branch and put a reference in the project description.
thx for the great project!