code: func (mt *MediaType) String() string {
  	var buf bytes.Buffer
  	for k, v := range mt.Params {
  		fmt.Fprintf(&buf, ";%s=%s", k, EscapeString(v))
  	}
  	return mt.ContentType() + (&buf).String()
  }
docs: // String implements the Stringer interface.
  //
  // Params values are escaped with the Escape function, rather than in a quoted string.