upnpc.c: --help and -h arguments

fixes #037

miniupnpc/Changelog.txt

@@ -1,6 +1,9 @@
 $Id: Changelog.txt,v 1.189 2013/10/07 10:04:55 nanard Exp $
 miniUPnP client Changelog.
 
+2013/12/09:
+  --help and -h arguments in upnpc.c
+
 2013/10/07:
   fixed potential buffer overrun in miniwget.c
   Modified UPNP_GetValidIGD() to check for ExternalIpAddress

miniupnpc/upnpc.c

@@ -506,6 +506,11 @@ int main(int argc, char ** argv)
 	/* command line processing */
 	for(i=1; i<argc; i++)
 	{
+		if(0 == strcmp(argv[i], "--help") || 0 == strcmp(argv[i], "-h"))
+		{
+			command = 0;
+			break;
+		}
 		if(argv[i][0] == '-')
 		{
 			if(argv[i][1] == 'u')