Setuptools-ext

What's Changed
* Ensure long metadata lines aren't wrapped. Closes 9 by wimglenn in https://github.com/wimglenn/setuptools-ext/pull/10


**Full Changelog**: https://github.com/wimglenn/setuptools-ext/compare/0.5...0.6

- remove a workaround that setuptools-ext was doing now that https://github.com/pypi/warehouse/issues/11220 is fixed

- Require setuptools >= 61.0.0 only on Python 3.7+, this forces support for reading metadata from `pyproject.toml` _when possible_ without constraining usage on older Python versions (which may still read their metadata from `setup.cfg`)

- header fields are case-insensitive
- more forgiving of accidentally using a string instead of a list
- avoid a redundant home-page and project-url duplication
- strip out any "UNKNOWN" fields stuck in there by distutils
- requires python 3.6+

- Initial release. Only bdist support for now, sdist will come later..