Implement upload and download of files via SCP. * `$connection->upload($localPath, $remotePath)` using [scp-send](https://www.php.net/manual/en/function.ssh2-scp-send.php) * `$connection->download($remotePath, $localPath)` using [scp-recv](https://www.php.net/manual/en/function.ssh2-scp-recv.php)
