improve makefile functionality

- added help text
- allowed output directories to be overridden
- streamlined install process
- removed unused targets
- made all targets PHONY

Makefile

@@ -1,17 +1,32 @@
-BIN	= $(DESTDIR)/usr/bin
-LIB	= $(DESTDIR)/usr/share/gridtracker
-APP	= $(DESTDIR)/usr/share/applications
-MAN	= $(DESTDIR)/usr/share/man/man1
-DOC	= $(DESTDIR)/usr/share/doc/gridtracker
+.DEFAULT_GOAL := help
 
-all:
+DESTDIR ?= ./build
+BIN ?= $(DESTDIR)/usr/bin
+LIB ?= $(DESTDIR)/usr/share/gridtracker
+APP ?= $(DESTDIR)/usr/share/applications
+MAN ?= $(DESTDIR)/usr/share/man/man1
+DOC ?= $(DESTDIR)/usr/share/doc/gridtracker
 
+.PHONY: help
+help:
+	@echo "Specify a target to build:"
+	@echo "  -> make install"
+	@echo "    install gridtracker in DESTDIR (default: ./build)"
+	@echo "  -> make clean"
+	@echo "    remove built files from DESTDIR"
+
+.PHONY: clean
 clean:
+	@echo "Cleaning $(DESTDIR)..."
+	rm -rf $(DESTDIR)/*
 
+.PHONY: install
 install:
-	install -d $(BIN) $(LIB) $(APP) $(MAN) $(DOC)
-	install -c -m 755 gridtracker.sh $(BIN)/gridtracker
-	install -c -m 644 gridtracker.desktop $(APP)/gridtracker.desktop
-	install -c -m 644 gridtracker.1 $(MAN)
-	install -c -m 644 LICENSE $(DOC)
+	@echo "Installing gridtracker in $(DESTDIR)..."
+	install -Dcm 755 gridtracker.sh $(BIN)/gridtracker
+	install -Dcm 644 gridtracker.desktop $(APP)/gridtracker.desktop
+	install -Dcm 644 gridtracker.1 $(MAN)/gridtracker.1
+	install -Dcm 644 LICENSE $(DOC)/LICENSE
+	mkdir -p $(LIB)
 	cp -r package.nw/* $(LIB)
+