title: Modify/Add property via custom IContractResolver
body: <p>I have a class:</p>
  
  <pre><code> public class MyClass
   {
      public MyEnum Foo{ get; set; }
   }
  </code></pre>
  
  <p>During serialization i'd like to change the output from</p>
  
  <pre><code>{
     "Foo": 1
  }
  </code></pre>
  
  <p>to </p>
  
  <pre><code>{
     "Foo": "EnumName"
  }
  </code></pre>
  
  <p>I've tried creating an IValueProvider but hit dead ends every way I go.  (My scenario is a bit more complicated than stated; I need to find a way to do this entirely within the IContractResolver.)</p>