Example:
Media::attach('app', array(
'path' => '/var/www/website/app/webroot/extradir',
'prefix' => 'extradir'
));
Media::attach('cdn', array(
'absolute' => true,
'path' => null,
'host' => 'http://my.cdn.com',
'prefix' => 'project1/assets'
));
Media::attach('cdn', array(
'absolute' => true,
'path' => null,
'host' => array('my.cdn.com', 'secure.cdn.com'),
'scheme' => array('http://', 'https://'),
'prefix' => 'project1/assets',
));
Media::attach('cdn', array(
'absolute' => true,
'path' => null,
'host' => array('my1.cdn.com', 'my2.cdn.com'),
'scheme' => 'http://',
'prefix' => 'project1/assets',
));