In an age of the banning of certain books in public libraries and schools, I recommend seeing “Big River,” Roger Miller’s musical based on Mark Twain’s “The Adventures of Huckleberry Finn.” It’s playing through June 11 at Mercury Theater, 3745 N. Southport Ave.Twain’s novel has been banned on numerous occasions since it was first published in the United States in 1885. Opponents have described it as trashy and racist. It uses the N-word more than 200 times and often shows enslaved Blacks being treated in torturous and …