Adds makefile target for creating the global lib dir

Makefile

@@ -4,6 +4,7 @@ PREFIX := /usr/local
 EXEC_PREFIX := ${PREFIX}
 BINDIR := ${EXEC_PREFIX}/bin
 DATAROOTDIR := ${PREFIX}/share
+LIBDIR := ${PREFIX}/lib
 MANDIR := ${DATAROOTDIR}/man
 MAN1DIR := ${MANDIR}/man1
 
@@ -12,13 +13,17 @@ build:
 	${GOCMD} build -ldflags "-w -s" -o ${BINARY}
 
 .PHONY: install
-install: install-bin install-man clean
+install: install-bin install-man install-module-dir clean
 
 .PHONY: install-bin
 install-bin: build
 	install -d ${DESTDIR}${BINDIR}
 	install -m 0755 ./${BINARY} ${DESTDIR}${BINDIR}
 
+.PHONY: install-module-dir
+install-module-dir:
+	-mkdir -p ${DESTDIR}${LIBDIR}/slope/modules
+
 .PHONY: install-man
 install-man: ${BINARY}.1
 	gzip -k ./${BINARY}.1