to do
/////

* Fill in docstrings for ABCs.

* Implement InspectLoader for BuiltinImporter and FrozenImporter.

    + Expose function to see if a frozen module is a package.

* Make sure that there is documentation *somewhere* fully explaining the
semantics of import that can be referenced from the package's documentation
(even if it is in the package documentation itself, although it might be best
in the language specification).