"I come from Des Moines. Somebody had to." And, as soon as Bill Bryson was old enough, he left. Des Moines couldn't hold him, but it did lure him back. After ten years in England, he returned to the land of his youth, and drove almost 14,000 miles in search of a mythical small town called Amalgam, the kind of trim and sunny place where the films of his youth were set. Instead, his search…