Extended inspect_().get_leaf(). NEW FUNCTIONALITY.

OLD: you could only call the method on a leaf:

    inspect_(leaf).get_leaf(0)
    inspect_(leaf).get_leaf(-1)
    ...

NEW: you can now call the method on a container:

    inspect_(voice).get_leaf(0)
    inspect_(voice).get_leaf(-1)
    ...

FUCTIONALITY: this now provides a one-line way of getting the first (or last)
leaf in or from any component.