title: How to reset a BehaviorSubject
body: <p>I have a <code>BehaviorSubject</code> that I would like to reset - by that I mean I want the latest value to not be available, just as if it was just created.</p>
  
  <p>I don't seem to see an API to do this but I suppose there is another way to achieve the same result?</p>
  
  <p>My desired behavior is that I need to emit events, and I'd like subscribers to get the latest event when they subscribe - if a particular manager is in a 'started' state.  But when this manager is 'stopped' the latest event should not be available (just like if it was never started in the first place).</p>