FugueSide
The side a node occupies relative to its FugueNode.parent in the Fugue tree.
Left — left child: the node was inserted just after a descendant of FugueNode.parent. Left children are traversed before the parent.
Right — right child: the node claims the space immediately after FugueNode.parent. Right children are traversed after the parent. Only right-side nodes carry a FugueNode.rightOrigin.