docs/cookbook: Add script->state connection recipe

Script definitions can connect a signal to a State transition; this is a
useful thing to document with a recipe in the cookbook.

doc/cookbook/examples/script-states.c

@@ -0,0 +1,44 @@
+#include <stdlib.h>
+#include <clutter/clutter.h>
+
+int
+main (int argc, char *argv[])
+{
+  ClutterActor *stage;
+  ClutterScript *ui;
+
+  gchar *filename = "script-states.json";
+  GError *error = NULL;
+
+  if (clutter_init (&argc, &argv) != CLUTTER_INIT_SUCCESS)
+    return 1;
+
+  ui = clutter_script_new ();
+
+  clutter_script_load_from_file (ui, filename, &error);
+
+  if (error != NULL)
+    {
+      g_critical ("Error loading ClutterScript file %s\n%s", filename, error->message);
+      g_error_free (error);
+      exit (EXIT_FAILURE);
+    }
+
+  clutter_script_get_objects (ui,
+                              "stage", &stage,
+                              NULL);
+
+  /* make the objects in the script available to all signals
+   * by passing the script as the second argument
+   * to clutter_script_connect_signals()
+   */
+  clutter_script_connect_signals (ui, ui);
+
+  clutter_actor_show (stage);
+
+  clutter_main ();
+
+  g_object_unref (ui);
+
+  return EXIT_SUCCESS;
+}