Fix PHPDocs.

Return tag of `Hoa\Database\IDal\WrapperStatement::execute()` should be `Hoa\Database\IDal\WrapperStatement` because `Hoa\Database\DalStatement` and `Hoa\Database\Layer\Pdo\Statement` return `$this` and not a boolean like the native method `execute`.

And `*Statement::fetchColumn()`'s parameter to `int` like on [php.net (PDOStatement)](http://php.net/manual/en/pdostatement.fetchcolumn.php). Moreover `string $column = 0` isn't good ;)