Feature Request: Superimpose larger-timeframe candlesticks

Is it possible to represent two candlestick charts of different time-frame using mplfinance ?

I see an example using bokeh from [this](https://kernc.github.io/backtesting.py/#example) repository.


The idea would be:
- Choose a lower-timeframe (e.g 5 Min)
- Choose a larger-timeframe (e.g 15 Min)

Then, inside each 15 Min bar would have 3 five-minutes bar

The issue names mplfinance but no source file, entry point, or test. Start by reviewing the existing charting API and the linked backtesting.py example to determine how lower- and higher-timeframe OHLC data should be supplied and rendered. Done means a documented, tested way to show three 5-minute bars inside each 15-minute bar.

Written by the indexing model from the issue text.