Yes, there are witches among us, or so they say. Not ''pointy black hat, pointy green nose'' witches, but the modern kind, the urban sophisticated witches, and this is their time of year. They seem to enjoy their moment in the sun, or the darkness, as the case may be. Here is Stacy Rapp, 30, of Brooklyn, slender, with many tattoos and a shock of red hair. Not a mole in sight.