Typically, a librarian?s response to clamor is a vigorous ?Shhh!,? but now those bespectacled professionals might respond by clapping, cheering, and perhaps even waving a cigarette lighter. The Central Branch of the Brooklyn Library has taken to sponsoring a series of free outdoor concerts on its newly refurbished stone steps. The first incarnation featured a clever mix of artists like Ladybug Transistors, the Mariachi Academy of New York, and DJ Kool Herc. Book ?em!