Finally fix #797

* enhance README.md to match current PyPA install process
* improve and expand pyproject.toml
  * build requires section
  * build excludes section
* improve and shrink setup.py
  * remove SdistCommand
  * suppress nonsense warnings
* pyproject.toml now does most of the heavy lifting
* requires updates to pip, pipx, and setuptools
  * the newer pip builds a virtual environment
  * it installs the build requirements in that venv
  * the build is then done in that venv
* fixes to tools/install\* scripts to build/test VM environment
* replaces argparse with duplicity/argparse311 globally