It's easy to forget how much fun driving can be until you get behind the wheel of something small and fast. Audi's prescription for curing the driving blues is the S3; a turbocharged, all-wheel drive subcompact with fun in its DNA. The reborn A3 arrived a couple of years ago with a new sedan bodystyle and now encompasses a 2-door cabriolet, a plug-in hybrid hatchback and this sassier S3. My …