The big TV event of the month--maybe of the year—is “The Underground Railroad,” a ten-part series on Amazon Prime Video, directed by Barry Jenkins and based on the Colson Whitehead novel.  It’s being called “the most ambitious take on American slavery since ‘Roots’” --that was on TV almost 40 years ago. Eric Foner comments; he wrote the book on the hidden history of the underground railroad: it’s called “Gateway to Freedom.”