As unlikely as it sounds that someone has made a taut and entertaining film about credit, that’s precisely what James D. Scurlock has done with “Maxed Out,” in which he delivers a punchy, well-reasoned account of America’s huge problem with debt, how we got there and what the stakes are. (P.S., Scurlock is not the guy who took on the fast-food industry in “Super Size Me.” That was Morgan Spurlock.)