title: Optional parameter in the middle of a route
body: <p>Is there any way to add an optional parameter in the middle of a route ? </p>
  
  <p>Example routes:</p>
  
  <pre><code>/things/entities/
  /things/1/entities/
  </code></pre>
  
  <p>I tried this, but it does not work:</p>
  
  <pre><code>get('things/{id?}/entities', 'MyController@doSomething');
  </code></pre>
  
  <p>I know I can do this...</p>
  
  <pre><code>get('things/entities', 'MyController@doSomething');
  get('things/{id}/entities', 'MyController@doSomething');
  </code></pre>
  
  <p>... but my question is:  <em>Can I add an optional parameter in the middle of a route?</em></p>