CUMMING — What has been described by many theater critics as one of the best American musicals in history began a three-week run at the Cumming Playhouse on Thursday. BK Productions presents “Gypsy: A Musical Fable,” based on the 1957 memoirs of Gypsy Rose Lee, a famous burlesque performer, actress and author in the 1940s and ’50s. The musical is based loosely on the book and focuses on Lee’s childhood and teenage years, growing up on the 1920s’ vaudeville stage under the direction of her mother, Mama Rose.