Log Message:
py-cssutils: update to 2.3.0.

v2.3.0
======

#7: Add support for a ``calc()`` within a ``calc()``.

v2.2.0
======

Minor cleanup.

Restored package version reporting when fetching URLs.

v2.1.0
======

Adopted `jaraco/skeleton <https://github.com/jaraco/skeleton>`_.

Delinted codebase.

Removed ``cssutils.VERSION`` and ``cssutils.__version__``.
Consumers wishing to know the version should use
``importlib.metadata.version('cssutils')``.

v2.0.0
======

New `maintainer <https://pypi.org/user/jaraco>`_ revives the project
and moves `hosting <https://github.com/jaraco/cssutils>`_ with
continuous integration testing.

Refreshed packaging.

Project now requires Python 3.6 or later.