Include Python 3.13 in test matrix

Also install minimal subset of PyObjC to speed
up venv creation, especially for Python 3.13
where there are no binary wheels for PyObjC (yet)

Version update

Implement support for python 3.12

This basically just implements 'find_spec' on the metapath finder
for included subpackages

Fixes #491

Prepare for release

Minor tweaks

Fix bad metadata

Some changes after running tox

Minor updatese after running testsuite

Attempt at a pyside6 recipe

This recipe doesn't work, the packaging for PySide6 is
once again different from the prevous versions requiring
a complete redesign of the recipe. Sigh...

Update version number