Issue #85: Reduce the number of modules in base_library.zip.
Issue #85: Wrap imp.get_magic() for Python 3.
Issue #85: Fix pyi_importers.py to use _frozen_importlib.
Issue #85: Fix CExtensionImporter to use _frozen_importlib module and to try multiple C extension suffixes.
Issue #85: Include encodings.ascii in the base_library.zip.