Allow custom TaskLoader2.load_tasks to consume arguments

[ktbarrett]

From here. The remaining arguments not parsed by the Command are passed to the TaskLoader. This would be a nice opportunity for the TaskLoader to be able to consume/modify arguments before the arguments are parsed by the main program.

Proposal

Allow the result of the TaskLoader2.load_tasks to be either List[Task] or Tuple[List[Task], List[str]] where in the tuple case the second result would be arguments.

Alternatives

Right now it's possible to mutate the passed in the argument list to get the desired effect. That is obviously not intended.

[schettino72]

@ktbarrett could you please provide an example.