Pack ctypes modules (preliminary pull request for review only -- not ready for pull)

This pull request is to review changes I've made to resolve issue #100, pack ctypes modules. I've packed the modules in each of the build libraries into a corresponding super-module (so for instance, ctypes-foreign-base.cma has all of its modules packed into Ctypes_foreign_base module). I've only got two of the many tests modified to build, but I wanted to put this online for review sooner than later. Things to notice:

* I've renamed the project ctypes to ctypes-base, to avoid a name collision with the existing ctypes.ml module
* Clients of the library will now awkwardly have to open Ctypes_base, Ctypes_foreign_{threaded,unthreaded} in their programs