Tweak in Lang class

Changed function line() a bit, so we can pass parameters to be parsed by translation. For example:

$this->lang->line('name', 'John');

Where:

$lang['name'] = 'How is %s?';

Result:

'How is John?'
First parameter is mandatory, don't change it.
`$args` must be an array, `array $args = NULL` for it would be ideal.