iterator.go
func (it *Iterator) Init(list *Skiplist) {
	it.list = list
	it.arena = list.arena
	it.nd = nil
	it.value = 0
}
func (it *Iterator) Init(list *Skiplist) {
	it.list = list
	it.arena = list.arena
	it.nd = nil
	it.value = 0
}
// Init associates the iterator with a skiplist and resets all state.