BOSTON (AP) — When David Arsenault takes down a worn, leather-bound 19th-century book from the winding shelves of the Boston Athenaeum, he feels a sense of awe — like he’s handling an artifact in a museum. Many of the half a million books that line the library’s seemingly endless maze of reading room shelves and stacks were printed before his great-great-grandparents were born. Among fraying copies of Charles Dickens novels, Civil War-era biographies and town genealogies, everything has a