19.1.0
Move test helpers into an utils module
Be consistent in calling slotted classes slotted
Consistently use "base class" and "subclass" (#436)
Check type of set_run_validators' arg
Implement attr.converters.default_if_none (#414)
Implement first class exception support (#500)
Remove _add_init
Fade to Black (#392)
Quench a bunch of warnings
Some new validators (#425)
Cache hash codes (#426)