cansequence: also show help for option "-?"

This avoids the "invalid option" error message in the auto generated
man pages.

| DESCRIPTION
|       ./cansequence: invalid option -- '?'

cansequence.c

@@ -273,7 +273,7 @@ int main(int argc, char **argv)
 		{ 0, 0, 0, 0 },
 	};
 
-	while ((opt = getopt_long(argc, argv, "ei:pq::rvh", long_options, NULL)) != -1) {
+	while ((opt = getopt_long(argc, argv, "ei:pq::rvh?", long_options, NULL)) != -1) {
 		switch (opt) {
 		case 'e':
 			extended = true;
@@ -312,6 +312,7 @@ int main(int argc, char **argv)
 			break;
 
 		case 'h':
+		case '?':
 			print_usage(basename(argv[0]));
 			exit(EXIT_SUCCESS);
 			break;