Asymmetric violin plot

[lee1043]

Add a new capability that violin plot can show different population of samples in two groups.

Potential references:

• https://stackoverflow.com/questions/64646449/how-to-create-asymmetric-violin-plot-in-python-using-matplotlib
• https://stackoverflow.com/questions/47409086/how-to-plot-two-violin-plot-series-on-the-same-graph-using-seaborn
• https://seaborn.pydata.org/generated/seaborn.violinplot.html
• https://stackabuse.com/seaborn-violin-plot-tutorial-and-examples/

[lee1043]

@msahn just a heads-up, that this capability is about to be merged to the master. Example usage is at the bottom of the sample notebook. Could you please take a look if the usage example makes sense to you or if you have any suggestion?

You should be able to use this new feature by install from the branch 787_ljw_pre-commit-hook-compliant or after the branch is merged to the master.

[lee1043]

@msahn the update now merged to the master.