4.x :: Multidimensional support and failures

[harikt]

This is related to #117 .

As we add type definition like

public function add(string $field, string $message, array $args = array()): FailureInterface

The message is no longer a string, it can become an array when it is using subfilter .

@pmjones have forseen this

things are going to be difficult and ugly

I am still checking whether there is a way.