v1.4.0

Added

• The to_dgl method is now being parallelised, speeding export up
  significantly.
• Added convenience functions save_dgl_graph and load_dgl_graph, which
  stores the Boolean train/val/test masks as unsigned 8-bit integers and
  handles the conversion. Using the dgl-native save_graphs and
  load_graphs causes an error, as it cannot handle Boolean tensors. These two
  convenience functions can be loaded simply as
  from mumin import save_dgl_graph, load_dgl_graph.