code: function RBTNode(key, value) {
    this.key = key;
    this.value = value;
    this.color = RED;
    this.parent = SENTINEL;
    this.left = SENTINEL;
    this.right = SENTINEL;
  }
docs: RBT Node
  @constructor
  @ignore
  @private
  @param {Buffer} key
  @param {Buffer} value
  @property {Buffer} key
  @property {Buffer} value
  @property {Number} color
  @property {RBTNode|RBTSentinel} parent
  @property {RBTNode|RBTSentinel} left
  @property {RBTNode|RBTSentinel} right