- move static package metadata to setup.cfg
- rename deprecated license_file field to license_files
Remove setuptools arguments:
- test_suite:
  Unneeded, as we disable the deprecated setuptools test command
Keep dynamic setuptools arguments:
- version/cmdclass:
  For writing static version info via versioneer
- install_requires:
  Some dependencies still depend on special environment variables
  instead of package "extra" dependency fields
- entry_points:
  The `gui_scripts` entry point should only be set when building wheels
  for Windows via `--plat-name={win32,win-amd64,cygwin}`
- data_files:
  All data files are optional and should not cause the build to fail if
  they are missing, eg. when building from sdist