refactor: change Node pointers to values & return (Node, bool)

[topi314]

This changes the method receivers of the Node type to values instead of pointers for non mutating methods & pointer return type as discussed in #19 (comment)

[topi314]

any chance you have some time to look at this? @amaanq

[amaanq]

Sorry @topi314, I think after thinking about this for a bit, it makes total sense to have the node methods pass the object by value, since none of them besides Edit mutate the Node, and they're pretty small, stack-allocated objects - with that, I would think it'd be more natural if newNode returned a tuple of (Node, bool), indicating if the Node is empty or not. Would you be up for adding that change in this PR too?

[topi314]

hey @amaanq, thanks for reconsidering on this matter. Yes I'd love to implement this and will try to do it in the next days.

[topi314]

I think this should be all changes required for refactoring.

I don't particularly like how I've written the tests, but this is prob the best we can do.
If you have any better idea let me know