By Toby Davis LONDON (Reuters) – After all the shocks and spills of the opening week, top seed Serena Williams remained impregnable as she unleashed her full arsenal to move almost effortlessly into the last 16 at Wimbledon on Saturday. A crushing 6-2 6-0 win over Japanese veteran Kimiko Date-Krumm offered a reminder that while her closest rivals in the women's game are often vulnerable to upsets, she is an immovable object at the top of the tree. …