title: Caliburn.Micro IEventAggregator Publish method missing an overload
body: <p>I'm working through some tutorials online learning Caliburn.Micro for the first time. Some of the tutorials are using the older 1.3.0 version, I'm using the newer 2.0.0.6 version which was the latest Nuget package which is likely the source of this discrepancy:</p>
  
  <p>When trying to publish the following message:</p>
  
  <pre><code>public void Red()
  {
  _events.Publish(new ColorEvent(new SolidColorBrush(Colors.Red)));
  }
  </code></pre>
  
  <p>The compiler throws an error saying that the overload wasn't found. The only overload for Publish that is available has the following signature:
      void Publish(object message, Action marshal)</p>
  
  <p>I got this to work by using the background worker thread method shown below but in my case it seems like overkill. Was the single parameter overload really removed from Caliburn.Micro?</p>
  
  <p>Also, the documentation is here: 
  <a href="https://caliburnmicro.codeplex.com/wikipage?title=The%20Event%20Aggregator">https://caliburnmicro.codeplex.com/wikipage?title=The%20Event%20Aggregator</a> 
  still show examples using the more basic, single parameter example where you simply pass a message. Is the documentation at this link the latest that correctly describes 2.0.0.6?</p>
  
  <pre><code>public void Red()
  {
  _events.Publish(new ColorEvent(new SolidColorBrush(Colors.Red)), 
  action =&gt; Task.Factory.StartNew(action));
  }
  </code></pre>
  
  <p>Finally, for bonus points:</p>
  
  <p>What is this 2nd parameter good for other than publishing the message on a background thread? Can someone give some other example(s) of what this overload can be used for? </p>