Use importlib.resources instead of pkg_resources (from setuptools)

[drvdputt]

This seems to work fine to resolve #277 . Let's see what the tests do.

[drvdputt]

In addition to the pull requests planned in #280 , can we pull this one in first?

[jdtsmith]

I know very little about packaging, but happy to merge this. Can you target this to the dev branch, which I just created as a clean branch from master?

[drvdputt]

The issue here is that we were using a packaging tool (always had to pip install setuptools) to deal with the import of our resource files (the example spectra and included science packs).

This was never a problem with the automated tests, since they seem to always have setuptools in their environment. This is why we never included setuptools as a dependency. So when setting up a virtual environment with python3 -m venv venv_name, it is not always guaranteed that setuptools is present.

With these changes, we use the native importlib, so one less dependency. I think we can merge this into dev. If any thing breaks, I'm sure all the other testing during development will reveal it.

[jdtsmith]

Great done. I'm pretty ignorant on all the flavors of setup* stuff. I can at least pip install a local directory though ;).