title: Issue with Special Characters in Retrofit 2 encoding
body: <p>So I'm looking to make a request to our api to log in a user, however there is a section that gets encoded in the Retrofit 2 method even though its set as <code>encoded = true</code>.  The base url is <code>https://testapi.test.ie</code>  The parameter I pass as the <code>serverext</code> is <code>mdc.php?action=</code>  However even after setting <code>encoded = true</code>  the resulting request body is: <code>https://testapi.test.ie/mdc.php%3Faction=login_user&amp;ts=1482924232742</code> where I require it to be: <code>https://testapi.test.ie/mdc.php?action=login_user&amp;ts=1482924232742</code> So I can see the issue is the <code>?</code> symbol. Below is my retrofit method, if anyone can help with this I would appreciate it in order to achieve the correct</p>
  
  <pre><code>@retrofit2.http.POST("/{serverext}login_user&amp;ts={timestamp}")
  @retrofit2.http.Multipart
  Call&lt;LoginResponseModel&gt; loginUser(@retrofit2.http.Path(value = "serverext", encoded = true) String server,
                               @retrofit2.http.Part(Constants.USER) String username,
                               @retrofit2.http.Part(Constants.PASS) String password,
                               @retrofit2.http.Path("timestamp") Long timestamp);
  </code></pre>