Arduino implementation of rfc6238 One-Time password as used by Google Authenticate

See a demo here: http://youtu.be/uYRjAbNJsXw https://twitter.com/russaus/status/163232099220996096

SHA hashing implementation from https://github.com/Cathedrow/Cryptosuite Real Time Clock library from https://github.com/maniacbug/RTClib