refactor packaging per PEP518

[prjemian]

Python's packaging recommendations are in transition. On the way to use of a pyproject.toml file to provide all static information (per PEP-517 and ultimately PEP-660), refactor the packaging to meet PEP518

Most of the difficulties have been demonstrated in a sample project:

• https://github.com/prjemian/ym2021_prj/issues/10
• https://github.com/prjemian/ym2021_prj/pull/11
• https://github.com/prjemian/ym2021_prj/issues/12
• https://github.com/prjemian/ym2021_prj/pull/13

A discussion on StackOverflow answers some related questions: https://stackoverflow.com/questions/62983756/what-is-pyproject-toml-file-for

[prjemian]

superseded by #230