date: implement the set date

[sylvestre]

coreutils/src/uu/date/src/date.rs

Line 234 in bfc9e13

unimplemented!();

isn't implemented.

It should be cross platform but starting with one platform first is fine.

Tests are in
https://github.com/uutils/coreutils/blob/8337179454d0c952746a980ee37a32340f510a46/tests/by-util/test_date.rs

[marcosatti]

I'm tackling this one if its not taken...

How is libc and winapi meant to be used here? I can see in uucore there is a public reexport but individual utilities are specifying their own copies anyway...