add possibility to cumulate or not progress to the parent task progress if parent_task_id is provided

Clarify reporting with sub-tasks and document new option linked to fix#43

that's a bit stupid if you ask me. but if it pleases you and finally makes this available... I've done it

For such trivial stuff which are not even errors but more your own preferences,
it would take much less time and effort for you to put it directly to your liking.
No real added value to involve me

other linting changes (extra whitespace ... no comment !!!!)