“Books,” wrote the poet Philip Larkin, “are a load of crap.” No doubt Larkin, one of the most gifted lyric poets of the 20th century and a career librarian at the University of Hull, was being ironic. But irony or no, the participants and sponsors of this Saturday’s National Book Festival vehemently disagree. Held every year for the last six years on the National Mall — rain or shine — the festival brings together marquee-name…