title: get value from custom attribute in editor template
body: <p>at the moment I have this:</p>
  
  <p>in the ViewModel:</p>
  
  <pre><code>[MyCustom(Foo = 23)]
  public int CountryId { get; set; }
  </code></pre>
  
  <p>in the Editor template:</p>
  
  <pre><code>&lt;%= Html.TextBox("", Model) %&gt;
  </code></pre>
  
  <p>how can I get the value (Foo=23) from my custom attribute (MyCustom) into the editor template ?</p>