Clean up the PyPI dist packages, remove unnecessary files, and
streamline the release process:
* Avoid adding extra unnecessary files to the repo; setup.py is code
and can copy the necessary files into place.
* Make sure README.md is included so we don't get an UNKNOWN
Description field.
* Add a long_description_content_type to avoid parsing errors on the
README.md file and rejecting the upload.
* Define the license and platform fields so they don't show up as
UNKNOWN either.
* Remove unnecessary pyproject.toml. This makes sense for most python
projects, but since I already have a Makefile with installation
rules (because I'm trying to be more compatible with git.git just in
case we ever get merged into it), the pyproject.toml file is
somewhat duplicative. Sure, the Makefile won't specify the exact
versions needed but...meh.
* Split the release target of the Makefile into github_release and
pypi_release substeps, to allow them to be run semi-independently.
Make the pypi_release run a few more steps for me.
Signed-off-by: Elijah Newren <newren@gmail.com>