Added silent mode and a manual page

Makefile

@@ -1,5 +1,23 @@
-subnetcalc: subnetcalc.c
-	gcc -std=c99 -Wall -pedantic subnetcalc.c -lm -o subnetcalc
+CC=gcc
+CFLAGS=-Wall -pedantic -std=c99
+LIBS=-lm
+OBJS=subnetcalc.o
+BINDIR=/usr/local/bin
+MANDIR=/usr/share/man/man1
 
-clean: subnetcalc
-	rm subnetcalc
+subnetcalc: $(OBJS)
+	$(CC) -o subnetcalc $(OBJS) $(LIBS)
+
+subnetcalc: subnetcalc.c
+
+install: subnetcalc subnetcalc.1
+	gzip -c subnetcalc.1 > subnetcalc.1.gz
+	install -g root -o root -m 0644 subnetcalc.1.gz $(MANDIR)/
+	install -g root -o root -m 0755 subnetcalc $(BINDIR)/
+
+uninstall:
+	rm $(MANDIR)/subnetcalc.1.gz
+	rm $(BINDIR)/subnetcalc
+
+clean:
+	rm subnetcalc $(OBJS) subnetcalc.1.gz