* Use types instead of imp.new_module.

I can follow up with https://docs.python.org/3/library/importlib.html#importlib.util.module_from_spec if need be.

* use source loader from importlib

* Revert "use source loader from importlib"

This reverts commit 1f255704f7bf618fb7e0432e1fccef6ee22364d4.

* use inspect.getsource, but alas

* placate linter

* use find_spec to resolve a module spec to a file path

* better function naming

* remove outdated comment