 By Kate Lamb, Lucy Craymer and Kanupriya Kapoor WELLINGTON Reuters - Thursdays shock resignation of New Zealand Prime Minister Jacinda Ardern, who altered the face of global politics when she was elected the worlds youngest female head of state, throws a spotlight on the punishing demands faced by women in power. Holding back tears as she made her declaration, the 42-year-old politician said she had next to nothing left in the tank and it was time to step aside after a challenging 5-12 ye... 