[Feature request] Extend facet_grid to support rows and cols arguments

[bcm0]

ggplot2 provides rows and cols with a newer interface https://ggplot2.tidyverse.org/reference/facet_grid.html This would be a great extension.

I struggle with the syntax for facets and especially the use of dot in complex statements. There are some examples in the docs https://plotnine.readthedocs.io/en/stable/generated/plotnine.facets.facet_grid.html but I don't know what these special strings like "func()" or "factor()" mean or where to find more information.