Merge: Fix light FFI in interpreter on OS X

Fix #1623 by removing the soname declaration (the soname was more of a placeholder at this time anyway). Also take this opportunity to remove the `-g` flag.

The fixes to the md5 modules update it to the latest style and use the nity/native pattern to avoid callbacks so it is light FFI compatible. This was used to test the interpreter on OS X.

Pull-Request: #1642
Reviewed-by: Jean Privat <jean@pryen.org>
Reviewed-by: Lucas Bajolet <r4pass@hotmail.com>