Use of deprecated dash-separated keys in setup.cfg

[andy-maier]

This project uses dash-separated keys in its setup.cfg file:

[metadata]
description-file = README.md

setuptools has deprecated the use of dash-separated keys back in 2021, and has recently made an attempt to remove the toleration support for dash-separated keys, in its version 78.0.1. See also the discussion in pypa/setuptools#4910.

Meanwhile, setuptools version 78.0.2 has added the toleration support for dash-separated keys back in, but it is still deprecated and projects that still use them should change to use underscore instead of dash.

[andy-maier]

Addressed by PR #44.