“He’s changing the narrative.” The new comedy, “American Fiction,” features a wickedly sharp and bitingly funny premise. The feature-length directorial debut of Cord Jefferson, a producer and writer on acclaimed series such as “Watchmen,” “Station Eleven” and “Master Of None,” the film is adapted from Percival Everett’s “Erasure,” a brilliant indictment of the way modern culture handles race, a pointed satire about the commodification of marginalized voices and a writer forced to confront himself and his own creative integrity.