This is the start of the work on RBTools 4.0. It drops support for

Python < 3.7 and adds official support for Python 3.10/3.11.
4.0 will largely focus on modern compatibility, internal architectural

improvements, and support for Apple Diff.
As part of the package modernization effort, our rbtools/__init__.py

has been updated to use our modern logic (first established in

beanbag-tools) for version building.

Successfully built packages.
Tested that our version gatekeeping logic in setup.py did the right

thing for Python 2.7, 3.6, 3.7, 3.8, 3.9, 3.10, and 3.11.