The World of Extreme Happiness *** and Big Love ****
         By: David ShewardThe devastating effects of sexism are examined in two fascinating Off-Broadway productions. The playwrights' styles vary Jennifer Lim: "The World of Extreme Happiness"but they each offer clear-eyed observations on how treating women as inferior can warp society. Frances Ya-Chu Cowhig's The World of Extreme Happiness at Manhattan Theatre Club takes place in contemp…