Dataclasses-json

Performance optimization via caching (175, 148). Thanks Germandrummer92 konstin

Introduce API for global config of encoders by type (139).

To elaborate, you can now define globally how to encode any unsupported
_type_, rather than have to specify for every individual _field_.

Fix nested optional type (167). Thanks RunOrVeith

Fix `from_dict` annotations (156). Thanks eqperes

Introduce API for undefined fields. Thanks RunOrVeith and
Germandrummer92

Fix api type hints. Thanks JoeyBG

Make type annotations visible to mypy. Thanks gward