Added a new signature for makeTime to create time_t from discrete elements

[Daemach]

I like this library. I needed to be able to create a time_t from discrete elements so this signature creates the tm struct to pass to the original.

[Bougakov]

@Daemach thanks a lot for this code - it helped me a lot when I was implementing a feature that calculated how much time is left between now and future events on the same day: https://github.com/Bougakov/wallclock/blob/master/wallclock.ino

[papillon81]

I did the exact same thing for that purpose. But in my code. So I highly support this request :+1: