“Bob Newhart: Unbuttoned” traces the life and career of the quiet comedian, who gained fame from his 1960 record album, then starred in hit sitcoms in the ’70s and ’80s. Clips from those shows and excerpts from his stand-up routines are supplemented by Newhart’s own comments, plus those of his wife, Ginnie, and a number of colleagues. “Bob is a regular guy,” says David Steinberg, who directed him in the ’80s show. “He just happens to be a genius at being a regular guy.”