Add internal (plumbing) ffrun wrapper

To allow for experimenting with functions from embedded library.

src/bin/saturnin.skel

     _ls_subcommands)    ls_subcommands ;;
     _lsfun)             ffoom lsfun ;;
     _lsmod)             ffoom lsmod ;;
+    _ffrun)             ffrun "$@" ;;
     *)                  subcommand "$@" ;;
 esac