Adds RPM Lua extensions based on "lib" functionality

     Change: rpm-lua-extensions-based-on-rpm-lib-functionality
     Purpose: Adds RPM Lua extensions based on "lib" functionality
     Reason: The RPM Lua implementation is part of "rpmio". Hence
                     it cannot use RPM "lib" functionality without
                     breaking the RPM library dependency hierarchy.
                     Nevertheless it is very useful to have RPM "lib"
                     functionality in RPM Lua. The lib/rpmluaext.[ch]
                     provides this now. It attaches additional
                     functionality into the RPM Lua scope from within
                     RPM "lib". Currently it mainly provides the
                     following essential methods: rpm.digest() for
                     calculating a message digest, rpm.signature() to
                     check the public key signature on a clearsigned
                     file or a file and its detached signature, and
                     rpm.query() to query the RPMDB similar to "rpm -q
                     --qf '[...]' [-a] [...]" directly from within Lua.