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/errors.c

@@ -1,7 +1,5 @@
 /* -*- mode: C; c-file-style: "gnu"; indent-tabs-mode: nil; -*- */
 
-/* Mutter X error handling */
-
 /* 
  * Copyright (C) 2001 Havoc Pennington, error trapping inspired by GDK
  * code copyrighted by the GTK team.
@@ -22,6 +20,12 @@
  * 02111-1307, USA.
  */
 
+/**
+ * SECTION:errors
+ * @title: Errors
+ * @short_description: Mutter X error handling
+ */
+
 #include <config.h>
 #include <meta/errors.h>
 #include "display-private.h"