Kwargs for everyone

I don't necessarily think this should be merged, but offering it anyways.

I wanted to be able to over-plot other data on the same figure, and style it however I want. Here I've introduced 3 new keyword arguments: 

* `point_kwargs` gets passed to the `plot()` command if plotting data points
* `hist_kwargs` controls the 1D histograms
* `contour_kwargs` controls the contour plotting