ResponseText represents texts of responses.

The text may be prefixed by a ResponseCode.

ResponseText is returned from TaggedResponse#data or UntaggedResponse#data for "status responses":

• every TaggedResponse, name is always "+OK+", "+NO+", or "+BAD+".
• any UntaggedResponse when name is "+OK+", "+NO+", "+BAD+", "+PREAUTH+", or "+BYE+".