Added another dynamic row_option to provide row collapse functionality.

Hi, I find this xlsx package great!! and Thank You. I had noticed that as part of the writeSheetRow function the $row_options has become partially dynamic. I needed to also make the outlineLevel dynamic to apply a multi-row collapse effect. I've added an examples file ex11-row-group-collapse.php to show it working. e.g. $row_options = array('collapse' => true, 'hidden' => true, 'outlineLevel' => 1); $writer->writeSheetRow('Sheet1', $row_data, $row_options);