header.go
func (h *RequestHeader) AddBytesKV(key, value []byte) {
	h.Add(b2s(key), b2s(value))
}
func (h *RequestHeader) AddBytesKV(key, value []byte) {
	h.Add(b2s(key), b2s(value))
}
// AddBytesKV adds the given 'key: value' header.
//
// Multiple headers with the same key may be added with this function.
// Use SetBytesKV for setting a single header for the given key.