Drop setup.py

[nbraud]

Followup on #55.

• Get rid of setup.py, which was made optional by Add support for setup.cfg-only projects pypa/setuptools#1675.
• Set a version requirement for setuptools.

[nbraud]

This is blocked on pypa/setuptools#1515, since we to either invoke the test and release commands, or change the development workflow (invoking pytest and twine directly).

[duckinator]

This is also blocked on pypa/pip#6041, for an equivalent to ./setup.py build.

[duckinator]

Whoops, didn't mean to close it. >.>

[duckinator]

It looks like the pep517 package provides this:

python3 -m pep517.check path/to/source  # source dir containing pyproject.toml

and

python -m pep517.build path/to/source  # source dir containing pyproject.toml

I think I'll experiment with making a little tool built on top of pep517+twine+the zipapp module which provides a coherent interface for wheel/sdist/zipapp builds and releasing wheel/sdist to pypi.

[nbraud]

@duckinator TBH, in the current state of things, the “small tool” could literally be a shell script calling pep517 and twine (though making it in Python will likely be nicer).

[duckinator]

@nbraud when you have a moment, could you rebase this? ❤️ (no rush, since we can't merge it yet, just would like a more accurate diff to see what the state of it is~)

[nbraud]

@duckinator Done; for what it's worth, you could also have done it, since PRs have “Allow edits from maintainers” checked by default, and there couldn't have been any conflict.

[duckinator]

Okay, nice, this PR is down to just locking down the setuptools version and removing setup.py like I thought it would be. :3