DjbletsJSONEncoderallowed models to define a to_json() method, which

would be called when an instance of that model was encountered. Since

this is useful outside of models, the encoder's been updated to support

this on any object, making it much easier to encode content in places

like integration or site configuration storage.
JSONField has also been updated to make use of DjbletsJSONEncoder,

bringing those same benefits to any models that use that.
In order to keep all existing encoder usage from changing any behavior

with datetimes, DjbletsJSONEncoder now acceps a strip_datetime_ms

parameter, defaulting to True for compatibility reasons. JSONField

turns this off.

Unit tests pass.
Tested that a JSONField I was using in Review Board was able to

serialize an object with a to_json method.