Add an institution where the person works/worked.

        Args:
            :param institution: name of the institution.
            :type institution: string

            :param start_date: the date when the person joined the institution, in any format.
            :type start_date: string

            :param end_date: the date when the person left the institution, in any format.
            :type end_date: string

            :param rank: the rank of academic position of the person inside the institution.
            :type rank: string

            :param record: URI for the institution record.
            :type record: string

            :param curated: if the institution has been curated i.e. has been verified.
            :type curated: boolean

            :param current: if the person is currently associated with this institution.
            :type current: boolean

def add_institution(self, institution, start_date=None, end_date=None, rank=None, record=None, curated=False, current=False):
        """Add an institution where the person works/worked.

        Args:
            :param institution: name of the institution.
            :type institution: string

            :param start_date: the date when the person joined the institution, in any format.
            :type start_date: string

            :param end_date: the date when the person left the institution, in any format.
            :type end_date: string

            :param rank: the rank of academic position of the person inside the institution.
            :type rank: string

            :param record: URI for the institution record.
            :type record: string

            :param curated: if the institution has been curated i.e. has been verified.
            :type curated: boolean

            :param current: if the person is currently associated with this institution.
            :type current: boolean
        """
        new_institution = {}
        new_institution['institution'] = institution
        if start_date:
            new_institution['start_date'] = normalize_date(start_date)
        if end_date:
            new_institution['end_date'] = normalize_date(end_date)
        if rank:
            new_institution['rank'] = rank
        if record:
            new_institution['record'] = record
        new_institution['curated_relation'] = curated
        new_institution['current'] = current
        self._append_to('positions', new_institution)
        self.obj['positions'].sort(key=self._get_institution_priority_tuple, reverse=True)