a method to delete a record in the table
         
        :param primary_key: string with primary key of record 
        :return: string with status message

def delete(self, primary_key):
        
        ''' 
            a method to delete a record in the table
         
        :param primary_key: string with primary key of record 
        :return: string with status message
        '''
        
        title = '%s.delete' % self.__class__.__name__
    
    # delete object
        delete_statement = self.table.delete(self.table.c.id==primary_key)
        self.session.execute(delete_statement)
    
    # return message
        exit_msg = '%s has been deleted.' % primary_key
        return exit_msg