Set up new return values for distributed processing

[Vaguery]

When an interpreter runs a program, it should be possible to return one of several useful values/types, plus information on how it was set up.

• program ID
• program
• step limit
• step stopped
• completed?
• one of:
  • top item on stack X at end
  • top item on binding X at end
  • top item on stack X in all steps
  • top item on binding X in all steps
  • all of stack X at end
  • all of binding X at end
  • all of stack X in all steps
  • all of binding X in all steps
  • all stacks at end
  • all bindings at end
  • …