Keys to Soil Taxonomy (13th)

[brownag]

create_KST() will need to be refactored for changes in formatting in the new version of the Keys that is forthcoming. I have a proof copy for testing, not sure on timeline for public release

[brownag]

Partially addressed by #63, which adds a new method create_KST13(). For now create_KST() still runs on a version of the 12th edition keys and produces some additional datasets related to diagnostic features and other materials outside the main order->subgroup keys