Declarative visualizations

[timothyb0912]

What

This package produces visualizations imperatively. It creates model diagnostic images by directly manipulating matplotlib. Matplotlib makes it very difficult to test the resulting images. I should switch to using declarative visualization methods and packages (e.g. plotnine and altair) because I can easily test the resulting images (altair) and image declarations (plotnine).

At the very least, I can begin by re-implementing the diagnostic plots using a declarative library and exposing those new plotting methods / objects. Then, once I've re-implemented all the plots, I can remove the old plotting methods.