type Comparer interface {
	Less(x Comparer) bool
}

define int key like this

type KeyInt int

func (k KeyInt) Less(x Comparer) bool {
	return k < x.(KeyInt)
}

1. NewSkipList
2. DeleteNode
3. First, get the key like cpp
4. Second, get the value like cpp
5. Insert
6. IsEmpty
7. LowerBoundNode, find the lower bound node, like cpp map, key >= find key
8. Search, SearchNode

1. Key, get the key
2. Value, get the value
3. Next, the next node
4. Prev, the prev node
5. NewSkipListNode

1. MaxLevel 32
2. level i+1/level i = 0.25