text: Title: ENH: Task return values to parameters
  Body: **Describe the solution you'd like**
  The return values are passable via queue (if multiprocessing) or via direct modification (if thread or main). These values need to be processed in Scheduler. Probably requires a new Argument type.
  
  The argument type can be named as ``ReturnArg`` and can be put to Parameters using the name of the task as the key or so.
  
  