Add pyproject.toml

[Corvince]

I think this is needed for packaging this up for pypi.

[rht]

Installation via the pyproject.toml by itself won't execute the imperative code that downloads the JS dependencies.

[jackiekazil]

Interesting... so then toml isn't a complete replacement for setup.py?

[rht]

It should be possible with plugin (at least for Poetry), but I don't know how do it yet for vanilla setuptools with pyproject.toml.

[wang-boyu]

pyproject.toml, setup.cfg and setup.py can probably be used together? This is the setup for Mesa-Geo.