Ken Burns’ latest documentary series is coming this fall: The Roosevelts: An Intimate History, a study of Theodore, Franklin and Eleanor Roosevelt that covers a century of American history in a seven-part, 14-hour epic look at the lives and contributions of three members of a single family. Early buzz has it as one of the very best efforts to ever emerge from the Burns shop, which is the highest praise possible. Tonight’s 30-minute preview serves as a teaser, as an appetizer, and, in this fractured TV landscape, one way to begin to build awareness and expectations months ahead of time. Check local listings.