Make --startup_notification also available as -startup_notification

All other options have a variant with just a single hyphen - be
consistent.

src/dunst.c

@@ -183,8 +183,8 @@ int dunst_main(int argc, char *argv[])
                 settings.print_notifications = true;
         }
 
-        settings.startup_notification = cmdline_get_bool("--startup_notification",
-                        0, "Display a notification on startup.");
+        settings.startup_notification = cmdline_get_bool("-startup_notification/--startup_notification",
+                        false, "Display a notification on startup.");
 
         /* Help should always be the last to set up as calls to cmdline_get_* (as a side effect) add entries to the usage list. */
         if (cmdline_get_bool("-h/-help/--help", false, "Print help")) {

src/option_parser.c

@@ -608,14 +608,14 @@ void cmdline_usage_append(const char *key, const char *type, const char *descrip
 
         if (!usage_str) {
                 usage_str =
-                    g_strdup_printf("%-40s - %s\n", key_type, description);
+                    g_strdup_printf("%-50s - %s\n", key_type, description);
                 g_free(key_type);
                 return;
         }
 
         char *tmp;
         tmp =
-            g_strdup_printf("%s%-40s - %s\n", usage_str, key_type, description);
+            g_strdup_printf("%s%-50s - %s\n", usage_str, key_type, description);
         g_free(key_type);
 
         g_free(usage_str);