[bd] Attachment Store for XenForo 2.0 2.1.3

This version includes support for XenForo 2.1.

It also makes it easier to use the same storage (s3, ftp, etc.) for all files in /data. Just add this into config.php:

PHP:

$config['fsAdapters']['data'] = function () {
    return \Xfrocks\AttachmentStore\Fs::getAdapterDefault();
};
$config['externalDataUrl'] = function ($externalPath, $canonical) {
    return 'https://s3.amazonaws.com/bucket/' . $externalPath;
};