

v0.2.1:

    * make CallStack drop references to stack frames once they have exited,
      to avoid creating lots of uncollectable garbage.

v0.2.0:

    * cleanly support yielding from within a restart context; previously
      this would leave the generator's retarts active.
    * require handlers to explicitly raise InvokeRestart(); this makes the
      non-local control flow more explicit.
    * add a proper RestartSuite class for grouping several restarts into
      a single context:
          * the RestartSuite is returned when entering its context, and
            can be used to invoke functions within the scope of only those
            restarts that it contains.
          * the decorator syntax for adding restarts is now a normal method
            on the RestartSuite object.
    * add a proper HandlerSuite class for grouping several handlers into
      a single context:
          * the decorator syntax for adding handlers is now a normal method
            on the HandlerSuite object.

