Re-Introduce Visitor Keyword

[ChrisIsKing]

In Jac 1 when declaring a node and making reference to the walker which is currently visiting you would utilize the visitor keyword. In jaclang we've since changed this to be here. That is fine, but less intuitive when thinking about your program in a data spacial manner. We're suggesting to re-introduce the vistor keyword for simplicity.

A walker visits a node, as such when referring to that walker from the perspective of a node, visitor is more intuitive.