The Audi A8 is the largest sedan offered by the German automaker. It's been a part of the Audi lineup since 1997 here in the U.S., and it's now in its third iteration, with a wider range of models offered as it climbs the social ladder into a class of vehicles that includes the Mercedes-Benz S-Class, the Lexus LS, the BMW 7-Series, and the Jaguar...