code: function SHAMap(version) {
    this.version = version === undefined ? 1 : version;
    this.root = this.version === 1 ? new SHAMapTreeNodeInner(0) :
      new SHAMapTreeNodeInnerV2(0);
  }
docs: SHAMap tree.
  @param {Number} version (inner node version number)
  @class