In 1900, several women vanish in southeastern Australia. When students and staff from a girls’ school near Melbourne go on a Valentine's Day trip to Hanging Rock in 1900, three young women and an instructor disappear without a trace. The film “Picnic at Hanging Rock,” directed by Peter Weir and adapted from Joan Lindsay’s 1967 novel, is an artsy psychological mystery that feels like it could have been made anytime. I…