“Cymbeline” is unanimously considered Shakespeare’s most difficult play to stage. That might be because it’s incredibly hard to follow on the page, even with the help of color-coded flow charts. The play includes a war, a decapitated head, poison, mistaken identity, the appearance of a Roman god and an ending scene with 17 revelations in a row. The Fiasco Theater Company of New York has fearlessly staged “Cymbeline” to rave reviews. The six-member ensemble brings their production to the campus of Duke University this weekend.