- update to 0.20.0:
* Fix #245, never introduce new nodes during discard.
* Fix #268, do not rely on well implemented __ne__ for keys in
pmaps, instead do explicit inversion of equality
comparison when checking for inequality.
* Officially support Python 3.12.
* Officially drop support for Python 3.7.
* Fix #273, build more types of wheels.
* Fix #282, add generic types to types
* Fix #281, defaultdict can now be frozen. NB! This is a
backwards incompatible fix since defaultdict was not
previously frozen.

to 0.17.0. Thanks @cool-RR for this!
* Fix #166, Propagate 'ignore_extra' param in hierarchy. Thanks
* Fix #154, not possible to insert empty pmap as leaf node with
* Python 3.4 is no longer officially supported since it is EOL
* Fix #157, major improvements to type hints. Thanks @je-l for
* Fix #121, regression in PClass.set()