Remove the current focused tree node from the tree, and return the zipper
focused on the next sibling. In case none exists focuses up on the
parent of the removed node.
If the zipper is focused on tree root returns Option.none().
A zipper without the previously focused node focused on next node, or failing that, on the parent node. If the zipper is focused on the tree root returns Option.none().
Remove the current focused tree node from the tree, and return the zipper focused on the next sibling. In case none exists focuses up on the parent of the removed node.
If the zipper is focused on tree root returns
Option.none().