Sundance always plays host to “Nice Movies”. They’re nothing revelatory, but they’re a fine bit of escapism with a good sense of humor and characters trying to be better people. Paul Downs Colaizzo’s Brittany Runs a Marathon is the best kind of Nice Sundance Movie. It’s got the beats of a rom-com, but with the edge of an indie held together by smart storytelling and great performances, especially from lead actress Jillian Bell. Although the stakes are technically nothing more than a young woman trying to get her life together, Brittany Runs a Marathon is …