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/util.c

@@ -1,7 +1,5 @@
 /* -*- mode: C; c-file-style: "gnu"; indent-tabs-mode: nil; -*- */
 
-/* Mutter utilities */
-
 /* 
  * Copyright (C) 2001 Havoc Pennington
  * Copyright (C) 2005 Elijah Newren
@@ -22,6 +20,12 @@
  * 02111-1307, USA.
  */
 
+/**
+ * SECTION:util
+ * @title: Utility functions
+ * @short_description: Miscellaneous utility functions
+ */
+
 #define _GNU_SOURCE
 #define _POSIX_C_SOURCE 200112L /* for fdopen() */