Like many others, I love Fred Astaire. There was even an international conference devoted to him  in Scotland this year. He was one of the 20th century’s greatest dancers. He was also one of its greatest singers, although he had a rather thin, reedy voice. He danced and sang his way into our hearts through a series of films from the 1930s through the 1960s, then on television through the 1970s. In his biographical essay, Fred Astaire (Yale Univ., $22), Joseph Epstein  presents a thumbnail sketch of the life of this extraordinary man.  Much of the book focuses on Astaire and his partners, beginning with Ginger Rogers, with whom Epstein believes he did greater work than he did with other dancers such as Audrey Hepburn, Cyd Charisse, and Judy Garland.