title: Extension method for adding value to bit field (flags enum)
body: <p>Instead of doing this to add a value to flags enum variable:</p>
  
  <pre><code>MyFlags flags = MyFlags.Pepsi;
  flags = flags | MyFlags.Coke;
  </code></pre>
  
  <p>I'd like to create an extension method to make this possible:</p>
  
  <pre><code>MyFlags flags = MyFlags.Pepsi;
  flags.Add(MyFlags.Coke);
  </code></pre>
  
  <p><strike>Possible?</strike> How do you do it?</p>