It’s 10 a.m. on a November morning; Roselyn Lionhart sits on a folding chair in front of Jackson Cathedral belting out an exhilarating rendition of "I Love My Baby." It is raining today and the crowds are thin. In the distance, through the mist, a Lucky Dog proprietor is angrily shooing away pigeons with a broomstick. A middle-aged woman dressed conservatively in a gray flannel suit walks by and drops some loose change in David Leonard’s opened guitar case as he...