Integration with reticulate

[jimjam-slam]

I've tested collateral by mapping R functions that in turn call python functions, and that's fine to some extent (I haven't tested mapping on a python function directly—I suspect I would need to modify the source to make it work, but I could be wrong).

But side effect management leaves something to be desired at the moment:

1. Python output streams aren't captured at all unless the python function call is wrapped in reticulate::py_capture_output().
2. Output streams captured in the above way come out as one long stream—that is to say, individual warnings or outputs aren't separated into a character vector.
3. Although reticulate::py_capture_output() allows the user to specify either stdout or stderr (or both), types of side effects aren't otherwise separated. In fact, it's not entirely clear to me yet (as I learn more python) whether python's and R's side effects map to each other 1:1 at all.

Ideally collateral would get to a place where python functions "just work" in a predictable and fairly reasonable way.