docs: Various fixes

clutter/clutter-settings.c

@@ -34,6 +34,14 @@
 
 typedef struct _ClutterSettingsClass            ClutterSettingsClass;
 
+/**
+ * ClutterSettings:
+ *
+ * <structname>ClutterSettings</structname> is an opaque structure whose
+ * members cannot be directly accessed.
+ *
+ * Since: 1.4
+ */
 struct _ClutterSettings
 {
   GObject parent_instance;