- We have splitted `Offset` into `Offset` and `OffsetState` (name
changes in consideration). The former is used to construct and convert
local or UTC date, and the latter is used to store the UTC offset
inside constructed values. Some offsets are their own states as well.
- This uses lots of associated types which implementation is still in
flux. Currently it crashes with debuginfo enabled. We've temporarily
disabled debuginfo from `Cargo.toml`.
- This technically allows a conversion to the local time, but not yet
tested.
Kang Seonghoon