Episode 5. The opening episode of this second week of Ken Burns’ Country Music documentary series, “The Sons and Daughters of America,” covers a very short period, from 1964-68. But when you remember what was happening during those pivotal, explosive years, that sharp focus makes sense. And when you’re looking at, say, women’s rights and civil rights, who better than to channel those respective concerns in the world of country music than, respectively, Lor