Strip control characters from News in the RSS feed

Without this we could get an UnserializableContentError exception like this:

Traceback:

File "/usr/lib/python3/dist-packages/django/core/handlers/exception.py" in inner
  41.             response = get_response(request)
File "/usr/lib/python3/dist-packages/django/core/handlers/base.py" in _get_response
  187.                 response = self.process_exception_by_middleware(e, request)
File "/usr/lib/python3/dist-packages/django/core/handlers/base.py" in _get_response
  185.                 response = wrapped_callback(request, *callback_args, **callback_kwargs)
File "/usr/lib/python3/dist-packages/django/contrib/syndication/views.py" in __call__
  48.         feedgen.write(response, 'utf-8')
File "/usr/lib/python3/dist-packages/django/utils/feedgenerator.py" in write
  248.         self.write_items(handler)
File "/usr/lib/python3/dist-packages/django/utils/feedgenerator.py" in write_items
  259.             self.add_item_elements(handler, item)
File "/usr/lib/python3/dist-packages/django/utils/feedgenerator.py" in add_item_elements
  309.             handler.addQuickElement("description", item['description'])
File "/usr/lib/python3/dist-packages/django/utils/xmlutils.py" in addQuickElement
  20.             self.characters(contents)
File "/usr/lib/python3/dist-packages/django/utils/xmlutils.py" in characters
  27.             raise UnserializableContentError("Control characters are not supported in XML 1.0")

Exception Type: UnserializableContentError at /pkg/tob/rss
Exception Value: Control characters are not supported in XML 1.0