title: Add UITextField to title view of navigation item
body: <p>How do you add a text field to the title view of a navigation item and have it sized correctly?</p>
  
  <p>It works fine if I do this with a search bar like this but I don't know how to get a text field to size itself in the same way as a search bar.</p>
  
  <pre><code>myViewController.navigationItem.titleView = [UISearchBar new];
  </code></pre>