title: How to stop and resume Observable.interval emiting ticks
body: <p>This will emit a tick every 5 seconds.</p>
  <pre><code>Observable.interval(5, TimeUnit.SECONDS, Schedulers.io())
              .subscribe(tick -&gt; Log.d(TAG, &quot;tick = &quot;+tick));
  </code></pre>
  <p>To stop it you can use</p>
  <pre><code>Schedulers.shutdown();
  </code></pre>
  <p>But then all the Schedulers stops and it is not possible to resume the ticking later. How can I stop and resume the emiting &quot;gracefully&quot;?</p>