???Vehicle??? for purposes of Iowa???s exemption statute, which allows a farmer to exempt a team and wagon or other vehicle that farmer uses to habitually earn his living, is that in or on which a person or thing is carried or may be carried, and is a means of conveyance; a wheelbarrow, a covered wagon, a Rolls-Royce, a patient mule, a man-of-war, and possibly a Pullman car or ocean liner is a ???