decode into map[string]interface{}

Hello, would be possible to add support to decode into `map[string]interface{}`. I need to decode a properties file into a generic `interface{}` but below code is returning an error. Is there a reason to only allow it to be a struct?
```
	if t.Kind() != reflect.Ptr || v.Elem().Type().Kind() != reflect.Struct {
		return fmt.Errorf("not a pointer to struct: %s", t)
	}
```