He turns it into a great story — about them. — By Michael Mechanic When Kwame Alexander talks, you can sense something irrepressible just under the surface — laughter, maybe, or swagger — dying to burst forth. It’s the same vibe the 12-year-old protagonist of his Newbery Medal-winning 2014 novel-in-verse, The Crossover, exudes on the basketball court. Alexander, 48, was a…