Last Thursday's fall equinox marked the official start of autumn, but for us, like many, it is Labor Day weekend that signals the change of the seasons.  We savored the last days of summer on the island of Nantucket, a "wee elbow of sand" some thirty miles off the coast of Cape Cod.  Once known round the globe as the whaling capital of the world, her wind-swept beaches, charming cobblestone streets and storied maritime history have drawn visitors to her shores for nearly two centuries.