Derive MKIT_DIR from $0 if unset

src/make.skel

 
 export MKIT_VERSION=__VERSION__
 
-export MKIT_DIR=${MKIT_DIR:-mkit}
+export MKIT_DIR=${MKIT_DIR:-$(dirname "$0")}
 export MKIT_LOCAL=${MKIT_LOCAL:-.mkit}
 
 . "$MKIT_DIR/include/mkit.sh" || die "failed to init; check if MKIT_DIR is set properly: $MKIT_DIR"