example::

            >>> log.msg('Hello, world.')

        You MUST avoid passing in Unicode on Python 2, and the form::

            >>> log.msg('Hello ', 'world.')

        This form only works (sometimes) by accident.

        Keyword arguments will be converted into items in the event
        dict that is passed to L{ILogObserver} implementations.
        Each implementation, in turn, can define keys that are used
        by it specifically, in addition to common keys listed at
        L{ILogObserver.__call__}.

        For example, to set the C{system} parameter while logging
        a message::

        >>> log.msg('Started', system='Foo')

        Ú