Please straighten out your supported Python versions and dependencies

I just came back to this after several years and there seems to be *zero progress* in terms of cleaning up Python version support or packaging. Meaning `setup.py` *still requires future pkg* even though several other places claim only py36 or later (and several variants thereof). This is getting ridiculous trying to maintain a package that won't let go of out-dated dependencies. The world moves on and even bionic has been declared lifeless. Please lurch forward into at least the early 21st century...

Start by auditing setup.py and the other Python-version and dependency declarations mentioned in the issue, especially the requirement for future. Define one consistent supported-version policy, remove outdated dependency constraints, and verify that the package metadata agrees across the project. Done means the supported Python versions and packaging dependencies are consistent and installable.

Written by the indexing model from the issue text.