Features
* Add Hook class. Allows to introduce custom handlers (175) [Julien Duchesne]
Fixes
* Add pre-commit to CI (187) [Stavros Korokithakis]
* Use correct singular/plural form of “key(s)” in error messages (184) [Joel Rosdahl]
* When ignoring extra keys, Or's only_one should still be handled (181) [Julien Duchesne]
* Fix Or reset() when Or is Optional (178) [Julien Duchesne]
* Don't accept boolens as instances of ints (176) [Brandon Skari]
* Remove assert statements (170) [Ryan Morshead]