public static function get_instance()
 {
     // If the single instance hasn't been set, set it now.
     if (null == self::$instance) {
         self::$instance = new self();
     }
     return self::$instance;
 }
    public function output($vars)
    {
        $sidebar = '<span class="header"><img src="images/icons/addonmodules.png" class="absmiddle" width="16" height="16" /> Example</span>
	<ul class="menu">
	        <li><a href="' . $modulelink . '">Demo Sidebar Content</a></li>
	        <li>Version: ' . parent::$version . '</li>
	    </ul>';
        parent::debug($sidebar, 'sidebar output');
        return $sidebar;
    }
/**
 * Output Client Area
 * @param  array $vars WHMCS vars
 * @return array       pagetitle, breadcrumb(array), templatefile, requirelogin (boolean), vars (array)
 */
function affcoupons_clientarea($vars)
{
    return AffiliateCoupons::OutputClient($vars);
}
function affcoupons_client_head($vars)
{
    return AffiliateCoupons::ClientArea()->head($vars);
}