Encode datetime as Timestamp in msgpack
decoding custom format is still supported for backward compat. Note that revision modify the exception type raised when attempting to encode a naive datetime object for both formats (json amd msgpack): it now raises a TypeError instead of a ValueError.
The ENCODERS/DECODERS constants have also been split to make clear which codecs are specific to the json format.
Migrated from D4690 (view on Phabricator)