registries is a Python package that provides classes for managing

the registration and lookup of classes, objects, or other state, backed

by unique lookup attributes. It originally comes from Djblets, but is

being split out and modernized.
This initial change sets up the packaging infrastructure, testing files,

and the initial package files. It does not include the registry

functionality, which will come in an upcoming change.

Successfully built a package.
Ran pytest and tox with the in-progress implementation change.