Lower package requirements.

We don't need Emacs 24.3 specifically.  It's enough to have any Emacs
24.x as long as we also have the `cl-lib` package.

I tried this under Emacs 23.1 too, but `font-lock-mode` seems to never
call my fontification code.  I'm not sure what's going wrong there.
Don't need so many demangling examples.