new: implement --version option

src/main.c

@@ -108,14 +108,20 @@ END:
 }
 
 int main(int argc, char **argv, char **envp) {
+  signal(SIGINT, SIG_IGN);
+  setlocale(LC_ALL, "");
+  textdomain("xcfg");
+
   if (getuid() == 0) {
     error(_("You should use this script as a regular user, not as root!"));
     return EXIT_FAILURE;
   }
 
-  signal(SIGINT, SIG_IGN);
-  setlocale(LC_ALL, "");
-  textdomain("xcfg");
+  if (argc >= 2 && strcmp(argv[1], "--version") == 0) {
+    success(_("Simple xorg configuration tool %s"), VERSION);
+    info(_("Licensed under GPLv3, see https://www.gnu.org/licenses/ for more information"));
+    return EXIT_SUCCESS;
+  }
 
   struct Desktop desktops[] = {
       {