- `Date/Time - Duration` is now supported. (duh!)
- `with_offset` methods have been added.
- `LocalResult` now implements common traits.
- `LocalResult` has several methods to propagate errors.
this makes the initialization from untrusted sources easier
(`off.ymd_opt(y,m,d).and_hms_opt(h,n,s).single()`).
- `num` dependency is gone. It was only used for floored division
and it is not hard to copy only that portion from num.
- `Duration + Date` (or so) was blocked by rust-lang/rust#7590,
which has been subsequently fixed.
- Removed unused `unsafe` checks.