text: Title: Donchian Indicator - Miscalculation
  Body: Hi, I think the Donchian Channels indicator (DC, a volatility indicator) isn't computing the right thing : the computation should be on the highest highs and the lowest lows, instead of on the closes. So the code therefore becomes : 
  
  Definition : 
  
      def donchian(high, low, lower_length=None, upper_length=None, offset=None, **kwargs):
  
  line 15 : 
  
      # Calculate Result
      lower = low.rolling(lower_length, min_periods=lower_min_periods).min()
      upper = high.rolling(upper_length, min_periods=upper_min_periods).max()
      mid = 0.5 * (lower + upper)
  