text: Title: Feature Request:
  Body: **Is your feature request related to a problem? Please describe.**
  I've used matplotlib.finance to plot ML models learning loss curves (candle plot is very informative to visualise such data, i can see max and min loss in batch, std etc. But your lib support only date (datetime timestamp) as df index, not a step number (int)
  
  **Describe the solution you'd like**
  Add additional paramether to mpf.plot - index_type='date' by default
  
  **Describe alternatives you've considered**
  I've used matplotlib finance in special env with old libs version. It works, but not comfortable
  
  **Additional context**
  