http://www.raywenderlich.com/12837/icloud-and-uidocument-beyond-the-basics-part-1
http://www.raywenderlich.com/12837/icloud-and-uidocument-beyond-the-basics-part-2
http://www.raywenderlich.com/12837/icloud-and-uidocument-beyond-the-basics-part-3
http://www.raywenderlich.com/12837/icloud-and-uidocument-beyond-the-basics-part-4