[DOC] visualisations not building

[slumnitz]

plot_local_autocorrelation(), spatial weights functionality and parts of via_functionality not building in docs.

[weikang9009]

Copied from https://github.com/pysal/splot/pull/64

@slumnitz I took another look at the readthedocs building process. It seems that geopandas is not properly installed using pip. At first, it complains about descartes (ModuleNotFoundError: No module named 'descartes'). After I explicitly included descartes in requirements_dev.txt, it complains about Missing package rtree``.

Not sure about the best way to proceed since conda install geopandas will use a lot of resources and readthedocs might not allow it .

[slumnitz]

@weikang9009 I think we should just include pip installs of descartes and rtree as requirements.