He’s taken on baseball, World War II, antisemitism in America, and so much more. But in a way, for Ken Burns, all were prelude to The American Revolution, the six-part, roughly 12-hour documentary that will debut on PBS next Sunday. It was, Burns says, “a 10-year labor of love” for him and co-directors Sarah Botstein and David Schmidt. We “won’t work,” Burns said, “on a more important project than this one.” And perhaps most interestingly of all, we learn a great deal about the people who