Add RTCZero::reset function

[brendandower90]

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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