Try to use Modules as namespaces

It doesn't quite work, yet; I'm still working on making something like
the following example work:

Module A.
  Parameter x : Type.
End A.

Module B.
  Export A.
End B.

Check B.x.
(* Toplevel input, characters 21-24:
Error: The reference B.x was not found in the current environment. *)
Use [Include] to get constants where we want them.