Riccardo Magliocchetti

@mlasch we decided to use `importlib-metadata` on all python versions to simplify things on our side. From the next release `importlib-metadata` is used instead of `pkg-resources`.

@mgorny Have you noticed that our tests fail with Python 3.9 against stdlib `importlib.metadata`? I think that's a bit more unfortunate than relying on a backport package.

> Not sure why that docs check is failing.. You are exporting more stuff and so something must be added to the sphinx ignore list