docs: def MAC(self,days,rev = 0):
      """ Comparing yesterday price is high, low or equal.
          return ↑,↓ or -
          與前一天 days 日收盤價移動平均比較
          rev = 0
            回傳 ↑,↓ or -
          rev = 1
            回傳 1,-1 or 0
      """
      yesterday = self.raw_data[:]
      yesterday.pop()
      yes_MA = float(sum(yesterday[-days:]) / days)
      today_MA = self.MA(days)
  
      return self.high_or_low(today_MA, yes_MA, rev)