Hilary Hahn is 25 years old, from Baltimore, smart, pretty, and she maintains a Web site that is something like a blog. Oh, yes, and she is a world-famous violinist. Last night, DCist was there when she gave an excellent recital in the Kennedy Center’s Concert Hall, with pianist Natalie Zhu. The program (.PDF file) combined some rare esoterica on the first half with more crowd-pleasing pieces on the second half. All of it was…