Column and row labels in legends

[kinyatoride]

Description

Hi, would it be possible to add a feature that sets column and row labels in legends? I think this is useful when you have many overlapped labels. This will be something similar to the features in subplots, so should be easier to understand for proplot users.

I am thinking of something like this. https://stackoverflow.com/questions/44071525/matplotlib-add-titles-to-the-legend-rows

Example code

ax.legend(collabels = ['col1', 'col2'], rowlabels =['row1', 'row2'])