Adds a new worksheet to a spreadsheet.

        :param title: A title of a new worksheet.
        :type title: str
        :param rows: Number of rows.
        :type rows: int
        :param cols: Number of columns.
        :type cols: int

        :returns: a newly created :class:`worksheets <gsperad.models.Worksheet>`.

def add_worksheet(self, title, rows, cols):
        """Adds a new worksheet to a spreadsheet.

        :param title: A title of a new worksheet.
        :type title: str
        :param rows: Number of rows.
        :type rows: int
        :param cols: Number of columns.
        :type cols: int

        :returns: a newly created :class:`worksheets <gsperad.models.Worksheet>`.
        """
        body = {
            'requests': [{
                'addSheet': {
                    'properties': {
                        'title': title,
                        'sheetType': 'GRID',
                        'gridProperties': {
                            'rowCount': rows,
                            'columnCount': cols
                        }
                    }
                }
            }]
        }

        data = self.batch_update(body)

        properties = data['replies'][0]['addSheet']['properties']

        worksheet = Worksheet(self, properties)

        return worksheet