“Mumblecore” is a film genre of sorts. In mumblecore movies, very little happens and everyone acts pretty much like you and me. They’re little, low-budget films with a sense of the absurd. Brothers Mark and Jay Duplass are mumblecore royalty, with films like The Puffy Chair, Baghead, and The Do-Deca-Pentathalon. They discuss their new TV show, Togetherness, which debuts on HBO this Sunday.