title: Class 'REST_Controller' not found with Codeigniter and REST API service
body: <p>I'm having a problem with the popular REST API controller maintained by Chris Kacerguis. 
  I've imported the three files Format.php, REST_Controller.php and rest.php and placed them in the proper locations in my codeIgniter file structure.
  I created a Users controller that looks like this: </p>
  
  <pre><code>&lt;?php
  
  require_once APPPATH.'libraries/REST_Controller.php';
  
  class Users extends REST_Controller{
      public function index_get()
      {
          // Display all users
          $this-&gt;response("Get method");
      }
      public function index_post()
      {
          // Create a new user
          $this-&gt;response("Post method");
      }
  }
  ?&gt;
  </code></pre>
  
  <p>I keep getting a error message that says: "Class 'REST_Controller' not found" when I navigate to my endpoint: <a href="http://localhost/api_test/index.php/users" rel="nofollow noreferrer">http://localhost/api_test/index.php/users</a></p>
  
  <p>Any idea what i'm doing wrong?</p>