Add a test for %%, mark formatting strings as done in documentation
Only display "---" in result set if resulting stack has >1 slot
Support (each) for strings as well as sequences
Drop syntax for sub-expression evaluation

- Now that [] always evaluates in sub-expression context, we don't
  need -X anymore.
Drop op_strlit, op_empty_list, expand op_const to push whatever
Rename op_close to op_tr_closure

- This so that there aren't collisions with lexical closures that are
  coming later.