DOC: documentation related to how we want this to evolve, standards, testing mechanism, etc.

[simonjayhawkins]

placeholder.

[hauntsaninja]

I wrote a tool called stubtest that's useful for testing stubs and is bundled with mypy (https://mypy.readthedocs.io/en/stable/stubtest.html). We use it over at typeshed. Figured I'd mention :-)