Add internal hashing API designed for the typelib

In multiple places in the typelib, but most importantly the directory,
we need some fast indexing.  Perfect hashing, as implemented by CMPH
(previous commit), is an exact fit for the problem domain.

Add an API built on top of CMPH which maps strings->guint16 (we just
need a guint16 for the typelib index).

https://bugzilla.gnome.org/show_bug.cgi?id=554943