def breadcrumb(crumb, coerce_to=None):
    """
    Usage::

        from navigation.decorators import breadcrumb

        @breadcrumb('greeting')
        def some_view(request):
            return 'Hello world!'

        @breadcrumb(lambda request: u'greeting for %s' % request.user.username)
        def some_view(request):
            return 'Hello %s!' % request.user.username

    .. note::

        By default the value returned by a callable is required to be a
        ``unicode`` object. If the function returns a model instance, its
        ``__unicode__`` method is *not* called. Use ``coerce_to=unicode``.

    :param crumb:

        A ``unicode`` string or a callable that returns it.

    :param coerce_to:

        Coerces *crumb* to given type. The value can be ``unicode`` or any
        callable that returns a ``unicode`` object.

    """
    def wrapper(view):
        @wraps(view)
        def inner(request, *args, **kwargs):
            return view(request, *args, **kwargs)

        if coerce_to is not None:
            inner.breadcrumb = (
                lambda *args, **kwargs: coerce_to(crumb(*args, **kwargs)))
        else:
            inner.breadcrumb = crumb
        return inner
    return wrapper
Usage::

        from navigation.decorators import breadcrumb

        @breadcrumb('greeting')
        def some_view(request):
            return 'Hello world!'

        @breadcrumb(lambda request: u'greeting for %s' % request.user.username)
        def some_view(request):
            return 'Hello %s!' % request.user.username

    .. note::

        By default the value returned by a callable is required to be a
        ``unicode`` object. If the function returns a model instance, its
        ``__unicode__`` method is *not* called. Use ``coerce_to=unicode``.

    :param crumb:

        A ``unicode`` string or a callable that returns it.

    :param coerce_to:

        Coerces *crumb* to given type. The value can be ``unicode`` or any
        callable that returns a ``unicode`` object.