Addie Morfoot Contributor Ken Burns attended the 29th annual Nantucket Film Festival, which concludes Sunday, to give audiences a glimpse of his latest PBS documentary “Leonardo da Vinci.” The two-part, four-hour doc — directed by Burns, his daughter Sarah Burns and his son-in-law David McMahon — explores the life and work of the 15th-century polymath. “Leonardo da Vinci,” which begins airing in November, marks the first project Burns has directed that unfolds entirely outside the continental United States.