title: IHttpActionResult and helper methods in ASP.NET Core
body: <p>I'm trying to move my web api 2 project to ASP.NET 5.
  But I have many elements that are not present anymore.</p>
  
  <p>For example <code>IHttpActionResult</code> or <code>Ok(), NotFound()</code> methods.
  Or <code>RoutePrefix</code>[]</p>
  
  <p>Should I change every <code>IHttpActionResult</code> with <code>IActionResult</code> ? 
  Change <code>Ok</code>() with <code>new ObjectResult</code> ? (is it the same ?)</p>
  
  <p>What about <code>HttpConfiguration</code> that seems no more present in startup.cs ?</p>