Support datetime

[Totktonada]

It is not offered ATM (2021-12-13), but AFAIK there is agreement on the representation in msgpack. See tarantool/tarantool#6660.

[ligurio]

Similar PR with UUID support - #104

[ligurio]

Documentation for msgpack extension:

• box, datetime: messagepack serialization - step.4 box, datetime: messagepack serialization - step.4 tarantool#6660
• perf: datetime serialization benchmark tarantool#6688
• https://github.com/tarantool/tarantool/wiki/Selecting-Datetime-MessagePack-serialization-schema