Write hierarchy for all GO Terms in obo file.

def prt_hier_all(self, prt=sys.stdout):
        """Write hierarchy for all GO Terms in obo file."""
        # Print: [biological_process, molecular_function, and cellular_component]
        items_list = set()
        for goid in ['GO:0008150', 'GO:0003674', 'GO:0005575']:
            items_list.update(self.prt_hier_down(goid, prt))
        return items_list