Retrieves all tasks currently assigned to this project.

def task_assignments(self):
        '''Retrieves all tasks currently assigned to this project.'''
        url = str.format(
            'projects/{}/task_assignments',
            self.id
        )
        response = self.hv.get_request(url)
        return [TaskAssignment(self.hv, tj['task_assignment']) for tj in response]