AT LAST, AT LAST — the sun was shining, the mercury hit 90-plus, and half a dozen of us lit out for Central Park, to strip down to as little as the law allows and gorge ourselves on good books and good company. In the shade near Strawberry Fields, in the open sun of Sheep Meadow, we lounged and laughed and read, and even made a few converts — three young women a few yards away saw us and were bare-breasted themselves instants later. It’s a movement! A revolution! Or at least one hell of a nice way to spend a summer afternoon.  Here are some photos of this year’s grand debut, with more to come…