title: How do I implement the VirtualFileSystem required by SharpZipLib.Portable?
body: <p>I would like to add the <a href="https://github.com/ygrenier/SharpZipLib.Portable" rel="noreferrer">SharpZipLib.Portable</a> library to my <code>Xamarin.Forms</code> PCL project.  I am targeting Android and iOS.  The documentation mentions that you must implement a <code>VirtualFileSystem</code> in order to use the library, but I do not know how to do that and I have been unable to find much information on this topic.  </p>
  
  <p>Has anyone used this library that can guide me in the steps required to use it?</p>