Function get_header_value

examples/server/httplib.h:1612–1614

template <typename T>
inline T get_header_value(const Headers & /*headers*/,
                          const std::string & /*key*/, size_t /*id*/ = 0,
                          uint64_t /*def*/ = 0) {}

template <>
inline uint64_t get_header_value<uint64_t>(const Headers &headers,