* New events:
  - ConfirmationNeededEvent is triggered when a pendable requiring
    confirmation is created.  This allows us to define an event handler for
    this event which sends the user notification.
  - SubscriptionEvent is triggered when a member is added to a mailing list.
    This lets us define an event handler which sends the welcome message.
* send_welcome_message() now takes a member parameter instead of an address,
  which lets us directly access the member's delivery mode and user display
  name (if the member has a user, which it might not in some cases).
* Use the list id in the pendable record instead of the list name for
  robustness (the latter can change but the former is permanent).
* Test more registration conditions.
* In the bin/runner command line switch handling, default `verbose` to None
  instead of False.  This makes it work better with nose's -E switch (log to
  stderr).
* In call_api(), if a POST, PUT, or PATCH method is used and data is None,
  encode the empty dictionary; seems like the behavior of urlencode() has
  changed, so this is safer.
* Fix style and pyflakes warnings.