title: Use response header as part of returned object with Retrofit
body: <p>I am using Retrofit + RxJava + GSON to consume a rest api for search. The way the API is built, it returns a list of objects and the total results as a header in the response (<code>total-results</code>):</p>
  
  <pre><code>@GET("search/events?eager=[competition,tv]")
      fun searchEvents(@Query("q") q: String, @Query("category") category: String, @Query("order") order: String): Single&lt;List&lt;Event&gt;&gt;
  </code></pre>
  
  <p>I would like to instead return Single, where SearchResult is:</p>
  
  <pre><code>SearchResult {
   var total: Int
  var events: List&lt;Event&gt;
  }
  </code></pre>
  
  <p>Is this possible?</p>