func (u *URL) QueryString() string {
	return string(u.URI.QueryString())
}
QueryString implements `engine.URL#QueryString` function.
package fasthttp
import "github.com/valyala/fasthttp"
type (
	URL struct {
		*fasthttp.URI
	}
)
func (u *URL) Path() string {
	return string(u.URI.Path())
}
func (u *URL) SetPath(path string) {
	u.URI.SetPath(path)
}
func (u *URL) QueryParam(name string) string {
	return string(u.QueryArgs().Peek(name))
}
func (u *URL) QueryParams() (params map[string][]string) {
	params = make(map[string][]string)
	u.QueryArgs().VisitAll(func(k, v []byte) {
		_, ok := params[string(k)]
		if !ok {
			params[string(k)] = make([]string, 0)
		}
		params[string(k)] = append(params[string(k)], string(v))
	})
	return
}