Reduce argument passing-down in the API

[trexfeathers]

Something for the future - too early while the API is still in flux

There are quite a lot of parameters that appear in MANY operations, because they are needed by something deeper in the call stack. Examples include: radius/zlevel/zscale and rtol/atol. This creates a lot of bloat and duplication across the public API.

I think it would be good if we could come up with alternative solutions so that we can simplify the signatures of a lot of GeoVista operations. The solution will depend on the circumstance, but here are some examples:

• Move more obscure tweaks into **kwargs, which could be documented in a single place
• Contain linked arguments (e.g. rtol and atol) in a named tuple of settings
• Activate settings using a context manager instead
• Restructure to make greater use of classes so that the settings become class attributes