This module lets you defer actions at run-time that will take place when the
control flow returns into an upper scope. Currently, you can:

    * hook an upper scope end with "reap"
    * localize variables, array/hash values or deletions of elements in
      higher contexts with respectively "localize", "localize_elem" and
      "localize_delete"
    * return values immediately to an upper level with "unwind", and know
      which context was in use then with "want_at"