Replace pkg_resources by importlib.metadata

[seignovert]

Hi,
Thanks for this nice module!

I'm working on a project that does not require setuptools and I'm getting an ModuleNotFoundError: No module named 'pkg_resources'.

This issue was introduced in #129 when the script tries to infer its version dynamically. A simple workaround is it to use importlib.metadata native library (for python ≥ 3.8 and already backported in requirements.in for python 3.7) instead of pkg_resources.

[gforcada]

Oh, thanks, sorry, I forgot to see this one, and I already created #143 and already merged #144 which is needed, otherwise importlib.metadata is not available.