There is no earthly reason to write about the new off-Broadway musical Romeo & Bernadette except that it’s very clever. Mark Saltzman has repurposed some 300 hundred years of Italian song—Giordani through de Curtis with side trips via Rossini, Bellini, Leoncavallo, Cannio and Falvo—as songs and lyrics of a thoroughly modern (albeit 1960s-retro) musical.