Add a pyproject.toml and test with latest pip

[jlstevens]

PEP 518 is now supported by pip pypa/pip#4144 and it looks like that made it into releases of pip >= 9.0.2.

We should add a pyproject.toml to specify autover as a build dependency and test with pip + git clone. If that works, we can consider whether we should get rid of embed_version and simply raise an exception that can suggest upgrading pip to users trying to install from a git repo in this manner.

[jlstevens]

Just as a reminder: if we do take this approach, autover will need to be listed as a build requirement for conda recipes.

[ceball]

We should add a pyproject.toml to specify autover as a build dependency and test with pip + git clone.

You're proposing to add autover as the dependency this way; if that works (i.e. works for setup.py develop, pip+git clone, etc), then would param still need to provide autover?

[jlstevens]

... then would param still need to provide autover?

I think so as you still need autover as a runtime dependency, not just as a build time dependency. Of course, our packages could depend on autover but as they depend on param anyway, they would keep getting it from there.