Add pyproject.toml minimal configuration

[roberto-arista]

Soon pip will require a pyproject.toml to install a package. Here I've added the minimal configuration for setuptools.

Deprecation Warning:

DEPRECATION: fontPens is being installed using the legacy 'setup.py install' method, because it does not have a 'pyproject.toml' and the 'wheel' package is not installed. pip 23.1 will enforce this behaviour change. A possible replacement is to enable the '--use-pep517' option. Discussion can be found at pypa/pip#8559

Discussion:
pypa/pip#8559

[justvanrossum]

I have no experience with this setup, but if this suppresses the warning and otherwise still works: why not.

It would be better to strip setup.py of all the bump smartness, and move all config to the pyproject.toml file, but maybe this can be done later.