As Noah Baumbach’s second film of 2015, “Mistress America” shows a director hitting his stride. A screwball comedy about the relationship between two young women in New York, “Mistress America” is stuffed with outlandishly funny moments grounded in the fatuousness of self-absorbed people. The movie follows Greta Gerwig as Brooke, a boundlessly energetic self-styled renaissance women with New York wrapped around her finger. As her widower father prepares to marry a divorcee mom (Kathryn Erbe), Brooke finds herself thrilled with the admiration of her college-aged stepsister-to-be, Tracy (Lola Kirke). Faced with a personal dream on the brink of collapse, Brooke, Tracy and a few friends pile into a car heading for Connecticut, where complications of every kind arise.