Convert Date/Time<T> to Date/Time<U>

[Kroisse]

rust-chrono has several methods which convert NaiveDate/Time to Date/Time<Off>, but there's no method which do Date/Time<T> to Date/Time<U>, where T and U are different Offsets.

There are two ways of converting the offset of the date/time object:

• Preserve all of other fields, and replace only the offset info. This behavior likes Python's datetime.replace(tzinfo=new_tz). The duration between the result and the original will be same as a distance of their offsets.
• Preserve the time, and adjust the date and time data. This behavior likes Python's datetime.astimezone(new_tz). They should have same UTC timestamp that the result and the original.

[Kroisse]

This could be critical, because there is no way to make today or now from FixedOffset.

[lifthrasiir]

This is now possible with with_offset. Closing.