Build and upload wheels to PyPI

[jcugat]

Closes #432

For now both sdist and wheel are built and uploaded, but as @graingert commented #432 (comment) I can drop the sdist if you want.

Tested locally and the wheel is built correctly, the only step I could not test is the upload with twine to PyPI.

[sethmlarson]

My 2 cents is we should be shipping universal wheels only as a testament to ensuring no C extensions. :)

[jcugat]

Happy to change it. Initially I left both types because I thought it would be a problem for old pip versions, but I've looked and wheel support was added in pip v1.4 released on 2013, so unless somebody is using an ancient version it should be fine.

I'm not sure if there are any other side-effects, but contrary to what @graingert mentioned in the original issue, flit actually ships both the wheel and the sdist: https://pypi.org/project/flit/#files

[sethmlarson]

Oh then let's do what flit does and ship both. I think I'm good to review this then! :D

[sethmlarson]

Thanks for submitting this! 🎉

[graingert]

https://github.com/takluyver/flit/blame/fbd7a0d20daffad158d3a80bd8fae183f20114f7/doc/cmdline.rst#L59

Yeah ok it looks like it does ship them both. I wonder why

[sethmlarson]

Probably because pip always favors wheels over sdist so it doesn't hurt if you're pushing a universal wheel? Then you're guaranteed compatibility if you do end up getting installed by an ancient pip version.

[tomchristie]

I don't think we need a requirement for this, right?

(We could choose to include a pip install twine wheel in the ./scripts/publish script tho)

[jcugat]

True, for some reason I thought twine was already in test-requirements.txt. I'll open a PR to remove it and will check inside ./scripts/publish if wheel is installed or not (similar to the other required tools).