Add --help option to fix manpage generation

This fixes #57.

src/fwup.c

@@ -151,6 +151,7 @@ static struct option long_options[] = {
     {"no-eject", no_argument,       0, '#'},
     {"framing",  no_argument,       0, 'F'},
     {"gen-keys", no_argument,       0, 'g'},
+    {"help",     no_argument,       0, '?'},
     {"list",     no_argument,       0, 'l'},
     {"metadata", no_argument,       0, 'm'},
     {"progress-low", required_argument, 0, '$'},
@@ -295,7 +296,7 @@ int main(int argc, char **argv)
     atexit(mmc_finalize);
 
     int opt;
-    while ((opt = getopt_long(argc, argv, "acd:DEf:Fgi:lmno:p:qSs:t:VvUuyz123456789", long_options, NULL)) != -1) {
+    while ((opt = getopt_long(argc, argv, "acd:DEf:Fgi:lmno:p:qSs:t:VvUuyz123456789?", long_options, NULL)) != -1) {
         switch (opt) {
         case 'a': // --apply
             command = CMD_APPLY;
@@ -408,7 +409,9 @@ int main(int argc, char **argv)
         case '9':
             compression_level = opt - '0';
             break;
-        default: /* '?' */
+
+        case '?':
+        default:
             print_usage();
             exit(EXIT_FAILURE);
         }