As sweet a story as you’d expect for the origins of the World’s Nicest Puppet, Being Elmo: A Puppeteer’s Journey just about manages to win you over with its saccharine rags-to-expensive-felt tale. Sure, it’s more of a celebration of the golden days of Jim Henson Productions than anything else, but with Elmo at the helm it was fairly unlikely this documentary was ever going to explore the back alleys of Sesame Street…