Added test to show effective value of arbitrary objects.

Note that this now magically works:

    >>> staff = Staff("c'8 d'8 e'8 f'8")
    >>> attach('color', staff[1], scope=Staff)
    >>> for x in staff:
    ...     x, inspect(x).get_effective_indicator(str)
    (Note("c'8"), None)
    (Note("d'8"), 'color')
    (Note("e'8"), 'color')
    (Note("f'8"), 'color')

This will be extremely useful.