Need help using 3rd party library Carbon (a date time framework) with Xautoload

Carbon github page, I've installed and have this directory structure: `/sites/all/libraries/Carbon/src/Carbon/Carbon.php`

I've tried Xautoload before with Migrate and got Class missing error, so I thought it was a problem with Migrate, but now I tried minimal setup and still can't autoload a php library. Here is the test-case:

File testautoload.info:

name = Test Autoload
core = 7.x

dependencies[] = xautoload
dependencies[] = libraries

version = 7.x-1.x

File testautoload.module:

/**
 * Test Xautoload functionality.
 */

/**
 * Implements hook_libraries_info().
 */
function testautoload_libraries_info() {
  $libraries['Carbon'] = array(
    'name' => 'Carbon',
    'download url' => 'https://github.com/briannesbitt/Carbon',
    'version' => '1.4.0',
    'xautoload' => '_testautoload_xautoload_callback',
  );

  return $libraries;
}

/**
 * Implements hook_menu().
 */
function testautoload_menu() {
  $items['testautoload'] = array(
    'title' => t('Test Xautoload'),
    'page callback' => '_testautoload_page_view',
    'access callback' => TRUE,
    'type' => MENU_NORMAL_ITEM,
  );

  return $items;
}

/**
 * Callback function from hook_libraries_info().
 */
function _testautoload_xautoload_callback($api) {
  $api->namespaceRoot('Carbon', 'src/Carbon');
}

/**
 * Callback function from hook_menu().
 */
function _testautoload_page_view() {
  $time = \Carbon\Carbon::createFromTimestampUTC(REQUEST_TIME);
}

Clear cache, navigate to `/testautoload` gives me this:

Fatal error: Class 'Carbon\Carbon' not found in /var/www/club411.fahri/htdocs/sites/all/modules/custom/testautoload/testautoload.module on line 46

I have libraries-7.x-2.1, PHP-5.3.27, Apache-2.2.25, is there other requirements I'm missing? How to debug this?

PS: why I needed Carbon is because of this http://stackoverflow.com/questions/13128854/php-datetime-class-change-fi...