Mordecai Richler, you've made a serious mistake. You're usually so funny, too. But this is no laughing matter. How could you, the editor of The Best of Modern Humor, cram samples of work by 64 authors into a 542 page book and not find room for anything by Jean Shepherd? (Knopf, the publisher of Richler's book, should have called it A Lot of Modern Humor.) . . .