code: def moving_average_convergence(data, nslow=26, nfast=12):
      
      emaslow = moving_average(data, nslow, type='exponential')
      emafast = moving_average(data, nfast, type='exponential')
      return emaslow, emafast, emafast - emaslow
docs: compute the MACD (Moving Average Convergence/Divergence)
      using a fast and slow exponential moving avg
      return value is emaslow, emafast, macd which are len(data) arrays