specify func argument and related cleanup (#183)

* specifies the function argument type in commands.h compared to leaving
  it unspecified. all the functions in cmd_t must have arg_t as it's
  argument.
* changes to commands.h will now trigger a rebuild - this restores old
  behavior prior to 12efa0e
* cg_quit now uses it's argument as exit status
* DestroyNotify invokes cg_quit rather than calling exit directly.
* Explicitly pass EXIT_SUCCESS to cgquit in keybinding

Co-authored-by: Berke Kocaoğlu <berke.kocaoglu@metu.edu.tr>

main.c

@@ -802,10 +802,10 @@ static void run(void)
 				break;
 			case ClientMessage:
 				if ((Atom) ev.xclient.data.l[0] == atoms[ATOM_WM_DELETE_WINDOW])
-					cg_quit();
+					cg_quit(EXIT_SUCCESS);
 				break;
 			case DestroyNotify:
-				exit(EXIT_FAILURE);
+				cg_quit(EXIT_FAILURE);
 				break;
 			case ConfigureNotify:
 				if (win_configure(&win, &ev.xconfigure)) {