Add a meaningful name and description to all sections/files in the API docs

https://bugzilla.gnome.org/show_bug.cgi?id=695641

src/core/screen.c

@@ -1,7 +1,5 @@
 /* -*- mode: C; c-file-style: "gnu"; indent-tabs-mode: nil; -*- */
 
-/* Mutter X screen handler */
-
 /* 
  * Copyright (C) 2001, 2002 Havoc Pennington
  * Copyright (C) 2002, 2003 Red Hat Inc.
@@ -26,6 +24,12 @@
  * 02111-1307, USA.
  */
 
+/**
+ * SECTION:screen
+ * @title: MetaScreen
+ * @short_description: Mutter X screen handler
+ */
+
 #include <config.h>
 #include "screen-private.h"
 #include <meta/main.h>