title: How cancel task with retrofit and rxjava
body: <p>I have rest api.</p>
  
  <pre><code>@Get("/serveraction")
  public Observable&lt;String&gt; myRequest(@Query("Data") String data);
  </code></pre>
  
  <p>I know, that okhttp has canceling functionality(by request object, by tag), but don't know how use it with retrofit and rxjava. What is the best way to realize canceling mechanism for network tasks with retrofit and rxjava?</p>