- The way ``bfg_view`` declarations are scanned for has been modified.
  This should have no external effects.

- An object implementing the ``IRenderer`` interface (and
  ``ITemplateRenderer`, which is a subclass of ``IRenderer``) must now
  accept an extra ``system`` argument in its ``__call__`` method
  implementation.  Values computed by the system (as opposed to by the
  view) are passed by the system in the ``system`` parameter, which
  will always be a dictionary.  Keys in the dictionary include:
  ``view`` (the view object that returned the value),
  ``renderer_name`` (the template name or simple name of the
  renderer), ``context`` (the context object passed to the view), and
  ``request`` (the request object passed to the view).  Previously
  only ITemplateRenderers received system arguments as elements inside
  the main ``value`` dictionary.