Transition to using `flit`

[pradyunsg]

should we choose to something that uses pyproject.toml like flit?

Originally posted by @brettcannon in #332 (comment)

Yes. :)

[brettcannon]

+1 from me 😄 . (I'm also willing to do the work or con/ask someone else like @derek-keeler who has been looking to contribute to do this 😁 ).

[pradyunsg]

Oh 100%. PRs very welcome!

[brettcannon]

I'm reopening this as I believe we said we would give folks a year to get build to a place that they could rely on it and I believe that's occurred.

[vishwin]

It's probably high time to move back to flit_core, especially since it can bootstrap itself.