HEATBy JOYCE CAROL OATESIt was midsummer, the heat rippling above the macadam roads, cicadas screaming out of the trees, and the sky like pewter, glaring.The days were the same day, like the shallow mud-brown river moving always in the same direction but so low you couldn't see it. Except for Sunday: church in the morning, then the fat Sunday newspaper, the color comics, and newsprint on your fingers.