Structure supporting both Python & CLI

[adebardo]

We should think ahead of a structure that will allow to make a mirror Python API for the same workflow, such as:

xdem.workflows.accuracy(dem=, coreg_method=, ...)
Having a single interface called by both would ensure we don't create differences between the two (easier to maintain and test), and that one simply links to the other. As the Python interface would need to return in-memory objects, the CLI should then essentially call the Python API, and simply wrap the reading/writing to file of inputs/outputs?

In this case, we might want to already adapt the current structure, and pass argument in xdem.cli directly to a Python API of the like of xdem.workflows.accuracy(), to avoid any re-structuring work down the road 😉.