Make debugging kittens a little nicer

Now debug() writes to the stderr of the parent kitty process instead of
a temp file.

kitty/screen.c

@@ -1219,6 +1219,11 @@ screen_handle_cmd(Screen *self, PyObject *cmd) {
     CALLBACK("handle_remote_cmd", "O", cmd);
 }
 
+void
+screen_handle_print(Screen *self, PyObject *msg) {
+    CALLBACK("handle_remote_print", "O", msg);
+}
+
 void
 screen_request_capabilities(Screen *self, char c, PyObject *q) {
     static char buf[128];