Deborah Harkness is the author of the bestselling novel “A Discovery of Witches” and its sequels, including the latest installment, “The Blackbird Oracle.” She’s also a professor of European history and Renaissance science, and she knows all about the lore of witches and vampires. Anne Strainchamps is a huge fan of these books, so she was eager to talk with Harkness about the real history of magical belief.