“The Birth of a Nation” was the Sundance sensation this year. Fox Searchlight bought the movie for $17.5 million, a record for the festival. The film’s about Nat Turner’s slave rebellion in 1831. It was written, produced and directed by Nate Parker, who’s never made a movie before. He also stars in it as Nat Turner. Parker took the title from the 1915 silent film about the civil war that made history for its racism as much as its cinematic innovations. Madeleine spoke with Turner at the Sundance Film Festival this week.