Upload attachment to a workitem

        :param filepath: the attachment file path
        :return: the :class:`rtcclient.models.Attachment` object
        :rtype: rtcclient.models.Attachment

def addAttachment(self, filepath):
        """Upload attachment to a workitem

        :param filepath: the attachment file path
        :return: the :class:`rtcclient.models.Attachment` object
        :rtype: rtcclient.models.Attachment
        """

        proj_id = self.contextId

        fa = self.rtc_obj.getFiledAgainst(self.filedAgainst,
                                          projectarea_id=proj_id)
        fa_id = fa.url.split("/")[-1]

        headers = copy.deepcopy(self.rtc_obj.headers)
        if headers.__contains__("Content-Type"):
            headers.__delitem__("Content-Type")

        filename = os.path.basename(filepath)
        fileh = open(filepath, "rb")
        files = {"attach": (filename, fileh, "application/octet-stream")}

        params = {"projectId": proj_id,
                  "multiple": "true",
                  "category": fa_id}
        req_url = "".join([self.rtc_obj.url,
                           "/service/com.ibm.team.workitem.service.",
                           "internal.rest.IAttachmentRestService/"])
        resp = self.post(req_url,
                         verify=False,
                         headers=headers,
                         proxies=self.rtc_obj.proxies,
                         params=params,
                         files=files)
        raw_data = xmltodict.parse(resp.content)
        json_body = json.loads(raw_data["html"]["body"]["textarea"])
        attachment_info = json_body["files"][0]
        return self._add_attachment_link(attachment_info)