Tonight, HBO airs “Six By Sondheim,” a retrospective documentary of Stephen Sondheim’s career.  Directed by Tony winner James Lapine, the documentary includes interviews with and archival footage of Sondheim himself, as well as performances by a star-studded group of artists. Audra joins a cast including Darren Criss, Jeremy Jordan, and America Ferrera. The documentary focuses on six of Sondheim’s most famous songs: “Opening Doors,” “Something’s Coming,” “Send in the Clowns,” “Being Alive,” “I’m Still Here” and “Sunday.”