Add RTCZero::reset function

[brendandower90]

This would be really simple to do but would save extra time. I have added it to the RTCZero.cpp file on my local machine, but it could be a feature that more people would be interested in.

void RTCZero::reset()
{
setTime(0,0,0);
}

[agdl]

What's the point of this function? you can simpy add it to your sketch if you need it. It's just one line of code