MINOR: contrib/iprange: add a network IP range to mask converter

This tool has remained uncommitted in my development tree for almost a year.
Just minor polish and commit.

It can be used to convert some geolocation IP lists to ACLs.
diff --git a/contrib/iprange/Makefile b/contrib/iprange/Makefile
new file mode 100644
index 0000000..b3c72ed
--- /dev/null
+++ b/contrib/iprange/Makefile
@@ -0,0 +1,13 @@
+CC       = gcc
+OPTIMIZE = -O3
+LDFLAGS  = -s
+
+OBJS     = iprange
+
+all: $(OBJS)
+
+%: %.c
+	$(CC) $(LDFLAGS) $(OPTIMIZE) -o $@ $^
+
+clean:
+	rm -f $(OBJS) *.o *.a *~