title: Retrofit: send multidimensional array / or nested hash in GET query
body: <p>I want to make a GET request to <code>/realties</code> path with some filtering parameters added to that request. Parameters may look like this:</p>
  
  <pre><code>?filter[num_rooms]=2&amp;filter[region_coordinates][0]=[50,65]&amp;filter[region_coordinates][1]=[51,62]
  </code></pre>
  
  <p>I can't find a way to send such nested parameters with Retrofit @GET request. I found that I can send only a Map of strings: <code>@QueryMap Map&lt;String,String&gt;</code></p>