title: Route group with optional parameter
body: <p>I'm wondering if it is possible to use optional parameters in a group prefix.</p>
  
  <p>Using it with <code>{parameter?}</code> like in any other route doesn't work:</p>
  
  <p></p>
  
  <pre><code>Route::group(array('prefix' =&gt; 'foo/{foo_id?}'), function() {
     Route::any('bar', 'ApiFooController@bar');
  });
  </code></pre>
  
  <p>I would like to catch both <code>foo/bar</code> and <code>foo/2/bar</code>.</p>
  
  <p>As much as I can see, it only works without the questionmark but then <code>foo/bar</code>(without the parameter) throws an error.</p>
  
  <p>I would like to avoid defining two seperate groups which would be a workaround. Maybe Important to note: <code>bar</code> is a custom function in addition to a resource so I'm not trying to define a resource (like <code>foo.bar</code>).</p>