code: func (h *Histogram) UnmarshalJSON(b []byte) error {
  	var s string
  	if err := json.Unmarshal(b, &s); err != nil {
  		return err
  	}
  	data, err := base64.StdEncoding.DecodeString(s)
  	if err != nil {
  		return err
  	}
  	h, err = Deserialize(bytes.NewBuffer(data))
  	return err
  }
docs: // UnmarshalJSON - histogram will come in a base64 encoded serialized form