New module `suntime` for sunrise and sunset time
Approximated calculation of sunrise and sunset time. Adapted from https://github.com/SatAgro/suntime.
This looks like a useful addition, however SatAgro/suntime is LGPL which is incompatible with micropython-lib's MIT license...
I started from scratch with the formula provided by Wikipedia's Sunrise equation and it works. I'll provide a new clean and neat code under MIT license in the following days.
I just pushed a commit with the new module implementation. I rebased it on datetime branch (see PR #449) because it depends on that.
Just rebased on top of datetime.