text: Title: How to add Horizontal Line in make_addplot?  make_addplot(rsi,panel='lower',color='g',hlines=[20,80])         
  Body: I have this code.
  
  ```python
   apds = [mpf.make_addplot(buy_signal,scatter=True,markersize=100,marker='^'),
                      mpf.make_addplot(sell_signal,scatter=True,markersize=100,marker='v'),
                      mpf.make_addplot(close_signal,scatter=True,markersize=100,marker='o'),
                      mpf.make_addplot(rsi,panel='lower',color='g',hlines=[20,80])         
  
    mpf.plot(self.df,addplot=apds,figscale=2,volume=False,type = type,
                   title= str(self.info)
                   )
  
  ```
  I want to put a horizontal line for my RSI. But there is a kwargs error which says hline is not found.
  