title: iOS6 Add some additional information to ABAdressbook
body: <p>I need to know if card of current person in address book was changed from my application.</p>
  
  <p>My best idea to accomplish this is to save some data or property inside <code>ABAddressbook</code>.</p>
  
  <p>How can I save some additional data in iOS 6 in a person's card?</p>