ZOOM! By Stephen Cole Minerva P. (for Petunia) Cavendish was going to do it. She vowed she would and now she was. Minerva was about to escape the stifling world of 1920. Her mother, Louisa Z. (for Zelda) Cavendish was the most successful producer on Broadway with hits that filled theatres from 38th Street all the way up to 59th. Zelda, as she was known on the Street, had discovered Jerome Kern. "Jerry," Zelda had told him, "get out of that lousy Princess Theatre and expand,"