A fair lady once said, `Let them eat cake!' the history books record, there on the shelf, We repeat, `Let them eat cake!"" and homemaker dear, make it yourself.'"" Mrs. Rushing was her college class poet; the type of poetry she writes indicates the market at which this is beamed-- plain American, the kind of cake that any mother would like to make for her family or a Church fair. There hasn't been (as far as we could research) a cake cookbook in more than five years and there are innumerable choices here: layer cakes: angel and sponge; coffee, spice and fruit; refrigerator; party cakes as well as offbeat (salt pork) recipes. There are also many fillings and frostings. It's for the Betty Crocker type cook who hasn't stooped to the Betty Crocker readymix and some of these seem almost as easy.