binding/binding.go
func RegisterCustomDecoder(fn CustomTypeDecoder, types []interface{}, fields []interface{}) {
	rawFunc := (func([]string) (interface{}, error))(fn)
	decoder.RegisterCustomType(rawFunc, types, fields)
}
func RegisterCustomDecoder(fn CustomTypeDecoder, types []interface{}, fields []interface{}) {
	rawFunc := (func([]string) (interface{}, error))(fn)
	decoder.RegisterCustomType(rawFunc, types, fields)
}
// RegisterCustomDecoder allows to define custom type decoders.