code: def joinMember(self, JoinInfo):
          
          JoinInfo.LinkID = self.__linkID
          postData = self._stringtify(JoinInfo)
          return self._httppost('/Join', postData)
docs: 팝빌 회원가입
              args
                  JoinInfo : 회원가입정보. Reference JoinForm class
              return
                  처리결과. consist of code and message
              raise
                  PopbillException