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/window.c

@@ -1,7 +1,5 @@
 /* -*- mode: C; c-file-style: "gnu"; indent-tabs-mode: nil; -*- */
 
-/* Mutter X managed windows */
-
 /*
  * Copyright (C) 2001 Havoc Pennington, Anders Carlsson
  * Copyright (C) 2002, 2003 Red Hat, Inc.
@@ -24,6 +22,12 @@
  * 02111-1307, USA.
  */
 
+/**
+ * SECTION:window
+ * @title: MetaWindow
+ * @short_description: Mutter X managed windows
+ */
+
 #include <config.h>
 #include "window-private.h"
 #include "boxes-private.h"