Edit visit method into Visitor\Asserter to easily extend/test it.

This PR improve readability, extensibility, testability for `Visitor\Asserter`
It seems we have to use this variable for exceptions like [this](https://github.com/stephpy/Ruler/blob/visitor_asserter_refactoring/Visitor/Asserter.php#L269)

Not sure it's a good idea, IMO `( $value, $out, $handle, $eldnah)` would suffice for exceptions and method behavior.