class_docstr: Extension of Trix with a signal line (ala MACD)
  
  Formula:
    - trix = Trix(data, period)
    - signal = EMA(trix, sigperiod)
  
  See:
    - http://stockcharts.com/school/doku.php?id=chart_school:technical_indicators:trix
code: def __init__(self):
      super(TrixSignal, self).__init__()
  
      self.l.signal = self.p._movav(
          self.lines[0], period=self.p.sigperiod
      )
  
file_path: backtrader/backtrader/indicators/trix.py
imports: from __future__ import absolute_import, division, print_function, unicode_literals
  from .None import Indicator, MovAv
label_desc: Use image node_id 1 to create a new TrixSignal object from inherited base classes: Trix with example: obj = TrixSignal()