At the Parker Hill Branch of the Boston Public Library Oct. 5, Roberto Mighty brought the dead to life. Mighty, a multimedia artist and filmmaker, spoke to an audience of 20 about his upbeat docuseries “World’s Greatest Cemeteries,” currently airing its second season on PBS. The show follows Mighty on his travels to cemeteries in the United States and beyond, interviewing experts and exploring the lives of historical figures who lie within the graves.