If you had a television set in the 1950s, there's a better-than-even chance that each week you were watching comic Sid Caesar. "I don't think there's anybody comparable now, and I don't think there's ever been anyone comparable," said writer David Margolick, the author of "When Caesar Was King: How Sid Caesar Reinvented American Comedy."And he was! As many as 20 million people tuned into Caesar's live weekly variety series, "Your Show of Shows." "If you had a store that was open on Saturday night, or you were staging live shows on Broadway, you were very unhappy with 'Your Show of Shows,' and you complained to NBC about it," Margolick said. "The whole culture really changed." A portrait of comedian, musician and television pioneer Sid Caesar c. 1952.…