In his new novel “The Underground Railroad,” Colson Whitehead reimagines a sick and savage period in American history and proves once again that fine fiction immersed in historical facts can often be more truthful – and more powerful – than nonfiction. Almost every schoolchild learns about the Underground Railroad – that secret network of houses, outbuildings and clearings that served as safe houses for slaves fleeing north, particularly in the wake of the 1850 Fugitive Slave Act that added the