Use Poetry for packaging

[JWCook]

I'm a fan of poetry, and I'd potentially like to use it for packaging this library if possible.

@jayvdb My main hesitation with this is what you mentioned in #221, regarding poetry making it inconvenient to run tests for downstream packaging. Have you found any good solutions (or compromises) for this in any of the other projects you've worked with?

[jayvdb]

Perhaps use poetry for everything except create the sdist with another tool which includes the tests? Previously I have used @dephell for that, but it is abandoned.

[JWCook]

After doing a bit more digging, I think we can make this work by using the include option (roughly equivalent to MANIFEST.in, if I understand correctly) instead of packages. Also, the per-format packages support added in python-poetry/poetry#1133 appears to also apply to include, although I don't see that in the docs yet.

Example:

include = [
    { path = "tests", format = "sdist" }
]

I noticed this in poetry's own pyproject.toml, recently updated as a result of python-poetry/poetry#3952.

Here's an example artifact I built using this config:
requests-cache-0.7.0.dev1.tar.gz

That appears to correctly include tests/ without installing it as a package. Does that look correct to you?

[jayvdb]

looks good!

[JWCook]

Sweet! I finished and merged these changes to master. The next release will probably be in about a month or two, fyi.