title: Count of observers in a Rx Subject
body: <p>With Rx, what is the best way to get the number of current observers in a Subject?</p>
  
  <p>I have a scenario where I want to publish a message, but only if there are observers.  If there are no observers, I need to do something else.</p>
  
  <p>To get around this issue, what I've done is created my own ISubject implementation and expose a count of an internal IObserver collection.  I'm sure there must be an out of the box way of doing this, I'm just not fully familiar with what Rx has to offer.</p>
  
  <p>Thanks!</p>