- update to 3.20.1:
* Fix call to ``get_declared_fields``: pass ``dict_cls`` again
* Add ``absolute`` parameter to ``URL`` validator and ``Url``
* Use Abstract Base Classes to define ``FieldABC`` and
``SchemaABC``
* Use `OrderedSet` as default `set_class`. Schemas are now
ordered by default.
* Handle ``OSError`` and ``OverflowError`` in
``utils.from_timestamp`` (:pr:`2102`).
* Fix the default inheritance of nested partial schemas
* Officially support Python 3.11 (:pr:`2067`).
* Drop support for Python 3.7 (:pr:`2135`).

- rename docs subpackage to the more common doc name
- Update to 3.19.0
* Add timestamp and timestamp_ms formats to fields.DateTime (#612). Thanks @vgavro for the suggestion and thanks @vanHoi for the PR.