[Feature Request] Wait for all current jobs to finish

[rubenhorn]

Why?
When running inside another job environment such as Slurm, the main process should wait for all tasks to finish before terminating.
Currently, this can be achieved through writing a loop over all IDs:

ID=$(./ts my-bin)
IDS+=($ID)
for ID in ${IDS[@]}; do
  ./ts -w $ID # Wait for the task to finish
done

What?
It would be more convenient to have a single option like --wait-all which implements this behaviour.