title: shrinkresource ,proguard etc in xamarin doesn't reduce my app size
body: <p>In android studio's <em>build.gradle</em> file,we can use <code>shrinkresources</code> set to <code>true</code> to shrinkify our app.Also can use <code>minifyenabled</code> and <code>proguard</code> options as well.</p>
  
  <p>But in xamarin, How can I use these options? </p>
  
  <p>I use proguard in my app as it referred in xamarin doc.but didn't find any use of it (I mean my app size didn't get reduced).My simple app is having around 18Mb in size.If anyone have experience using proguard in xamarin,please paste a sample file here also explain how you accomplished this.So others can also benefited.</p>