Refactor the examples to compile with a C++11 compiler

example/hello.cc

@@ -12,7 +12,7 @@ int main(void)
 {
     Server svr;
 
-    svr.Get("/hi", [](const auto& /*req*/, auto& res) {
+    svr.Get("/hi", [](const Request& /*req*/, Response& res) {
         res.set_content("Hello World!", "text/plain");
     });