DEV: First ~working kwarg_fetch
DEV: First ~working kwarg_fetch

Worked ok with hacky interactive session test. Remains to be tested
 on live code (primarily looking at utils.symm, but might be
 useful looking back at, e.g., utils.inertia, where there's a lot
 of chained code)

Still (likely?) needs to be robustified against missing optional
 arguments.

bskinn/opan,bskinn/opan