'Parse the new CodeResponse XML format. When successful, sets:
self.initial_display
self.answer (an answer to display to the student in the LMS)
self.payload'

def _parse_coderesponse_xml(self, codeparam):

    grader_payload = codeparam.find('grader_payload')
    grader_payload = (grader_payload.text if (grader_payload is not None) else '')
    self.payload = {'grader_payload': grader_payload}
    api_key = getattr(self.capa_system, 'matlab_api_key', None)
    if (api_key and (self.xml.find('matlabinput') is not None)):
        self.payload['token'] = api_key
        self.payload['endpoint_version'] = '2'
        self.payload['requestor_id'] = self.capa_system.anonymous_student_id
    self.initial_display = find_with_default(codeparam, 'initial_display', '')
    _ = self.capa_system.i18n.ugettext
    self.answer = find_with_default(codeparam, 'answer_display', _(u'No    answer    provided.'))
