title: What type is the subscriber in Observable.create((subscriber) => { ... }) in angular 2
body: <p>I've been pulling my hair out on this one. Has anyone figured out what type the subscriber is in the Angular 2 typescript code block below? </p>
  
  <pre><code>let obs: Observable&lt;string&gt; = Observable.create((subscriber) =&gt; { ... }) 
  </code></pre>