Susan Sanders and Russ Simmons are of one mind about "Maggie's Plan," a new comedy from writer/director Rebecca Miller ("Personal Velocity)" and starring Greta Gerwig ("Frances Ha"), Ethan Hawke ("Boyhood") and Julianne Moore ("Still Alice"). Gerwig plays a college professor who wants to have a child...but not, necessarily, get married. It aims at charm and whimsy over substance.