pass style_kwds into vba_choropleth()

[jGaboardi]

Seem like adding a style_kwds keyword argument to vba_choropleth() and then passing into gdf.plot(color=rgba, ax=ax) seems to be low hanging fruit that would provide nice customization. Thoughts, @martinfleis?

cc @jvtcl

[knaaptime]

fine if you want to make the change, but tbh I'd rather focus on the overhaul of splot so we can make sure all the pieces keep moving. I know we've got a handful of viz updates in the mix to update, so i'd put this near the bottom of the priorities list

(but that's also because I subscribe to the tufte-ian idea that you should avoid bivariate maps since they are cognitively overloading, usually done wrong, and tend to "produce ambiguous representations that convey information poorly" :P).

Though it would be a killer gsoc project for a student to put together a bunch of examples of how to do bivariate maps well using splot by, like, recreating the examples from here

[jGaboardi]

@knaaptime Seems like we could simply add in the keyword and pass directly into the plotting function. IMO, no tests are even needed since it's a GeoPandas thing at that point. If you agree, I think it is a no brainer to add – and I will do that. If there would be any kind of testing needed for this addition, then I agree it would be better to hold off for now. Let me know.

[martinfleis]

Let's put it it on hold until splot-focused month as per last PySAL call.