When you want to make a complicated thing simple, you break it down to the ABCs. When you want to get a handle on an event as sprawling as Jazz Fest, the same logic applies. Here’s the rundown—the headliners, the gospel acts, the contingent from Acadiana, the brass bands, the trad jazzers and more. Some are the acts you’ve known for all these years; some are new to Jazz Fest, but the odd...