title: Control sticky post date
body: <p>When I stick a post in the backend, I want it to be added a <code>meta_key</code> and <code>meta_value</code>. In other words, to control the date when the post has been marked as sticky, I want to add a <code>meta_key</code> like <code>date</code> and a <code>meta_value</code> like <code>date( 'm/d/Y H:i:s')</code>.</p>
  
  <p>I think it is possible with hook and <code>add_action</code>, but I don't know how. Is there a way to do that?</p>