binding/binding.go
func Register(contentType string, fn Binder) {
	lock.Lock()
	defer lock.Unlock()

	binders[strings.ToLower(contentType)] = fn
}
func Register(contentType string, fn Binder) {
	lock.Lock()
	defer lock.Unlock()

	binders[strings.ToLower(contentType)] = fn
}
// Register maps a request Content-Type (application/json)
// to a Binder.