added graclus boilerplate

test/test_graclus.py

+import pytest
+import torch
+from torch_cluster import graclus_cluster
+
+
+def test_graclus():
+    edge_index = torch.LongTensor([[0, 0, 0, 1, 2, 3, 3, 3, 4, 5, 5, 5, 6, 6],
+                                   [2, 3, 6, 5, 0, 0, 4, 5, 3, 1, 3, 6, 0, 3]])
+    edge_attr = torch.Tensor([2, 2, 2, 1, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2])
+
+    graclus_cluster(edge_index, edge_attr)

torch_cluster/__init__.py

 from .functions.grid import sparse_grid_cluster, dense_grid_cluster
+from .functions.graclus import graclus_cluster
 
 __version__ = '0.2.6'
 
-__all__ = ['sparse_grid_cluster', 'dense_grid_cluster', '__version__']
+__all__ = [
+    'sparse_grid_cluster', 'dense_grid_cluster', 'graclus_cluster',
+    '__version__'
+]

torch_cluster/functions/graclus.py

+def graclus_cluster(edge_index, edge_attr=None, batch=None):
+    pass