code: function Cursor (db, query, execFn) {
    this.db = db;
    this.query = query || {};
    if (execFn) { this.execFn = execFn; }
  }
docs: Create a new cursor for this collection
  @param {Datastore} db - The datastore this cursor is bound to
  @param {Query} query - The query this cursor will operate on
  @param {Function} execFn - Handler to be executed after cursor has found the results and before the callback passed to find/findOne/update/remove