title: Retrofit API to retrieve a png image
body: <p>Hi I am new to Retrofit framework for Android. I could get JSON responses from REST services using it but I don't know how to download a png using retrofit. I am trying to download the png from this url:
   <a href="http://wwwns.akamai.com/media_resources/globe_emea.png" rel="noreferrer">http://wwwns.akamai.com/media_resources/globe_emea.png</a>. 
  What should be response Object to be specified in the Callback&lt;> to achieve this.</p>