Add optional --task-list flag when starting workers. This used to be in the Luigi config file.
0.11
register_activity_worker()` now takes the full SWF activity object as an argument (instead of just the activity ID). also, `register_activity_worker()`is called before complete().
0.10
Added optional free-form identity strings to deciders and activity workers. Activity workers previously provided the worker index as the identity, but now the worker index is appended to the given identity string.
0.9
added "retry" signal (signal name is "retry", input is SWF Activity ID)