code: function Arm(args) {
      this.count = args && args.count || 0
      this.sum = args && args.sum || 0
    }
docs: ////////////////////////////////////////////////////////////////////////// Arm - one of the multi-armed bandit's arms, tracking observed rewards. // ////////////////////////////////////////////////////////////////////////// 
  @param {object} [args]
  @param {int} [args.count] - number of attempts on this arm
  @param {number} [args.sum] - total value accumulated on this arm
  @constructor