You can almost hear the music — Highway to the Dangerzone. San Antonio Mayor Julian Castro, like a young fighter jock in Top Gun, is clearly on a fast political trajectory, straight up. After his star turn at the Democratic National Convention, where the 38-year-old politico introduced himself nationally with a keynote address, word is he’s writing a memoir. The book should be on the shelves by the midterm elections in 2014. The San Antonio Express-News reports that New York-based Little, Brown and Co. will publish the autobiography. It’ll be written in English and Spanish and there’ll be an audio version.