text: Title: output to buffer
  Body: i need to save to io.buffer
  something like:
  
  ```python
  buf = io.BytesIO()
  mpf.plot(
  candles,
  type='candle',
  mav=(3, 6, 9),
  volume=True,
  show_nontrading=True,
  figratio=(6, 6),
  title="Graph",
  style='yahoo',
  savefig=buf
  )
  buf.seek(0)
  ```
  