in Bbcode.php search
public function notags($var = '')
and add'[usr]' => '',
'[/usr]' => '',
and search
protected function replacements()
and add'usr' =>[
'from' => '#\[user=(.*?)](.*?)\[/user\]#is',
'to' => '<a href="/profile/?user=$1">$2</a>',
],