When Jimmy Carter nearly bounds out of a hotel armchair to greet a journalist, it’s refreshing to see that the 90-year-old former president has not been passing the time – like so many of us these days – deep in a smartphone. Instead, he’s holding a book, a murder mystery by P.D. James. Carter has been an avid reader all his life, and he is certainly no stranger to the written word. He has just published his 29th book, “A Full Life: Reflections at Ninety” (Simon & Schuster; 257 pages; $28). It’s a sweeping and often tender overview of his life in which he guides readers through his hardscrabble boyhood in the mostly African American community of Archery, Ga.