code: func isScannable(t reflect.Type) bool {
  	if reflect.PtrTo(t).Implements(_scannerInterface) {
  		return true
  	}
  	if t.Kind() != reflect.Struct {
  		return true
  	}
  
  	// it's not important that we use the right mapper for this particular object,
  	// we're only concerned on how many exported fields this struct has
  	m := mapper()
  	if len(m.TypeMap(t).Index) == 0 {
  		return true
  	}
  	return false
  }
docs: // isScannable takes the reflect.Type and the actual dest value and returns
  // whether or not it's Scannable.  Something is scannable if:
  //   * it is not a struct
  //   * it implements sql.Scanner
  //   * it has no exported fields