DGL release and change logs

Refer to the roadmap issue for the on-going versions and features.

0.1.3

Bug fix

Compatible with Pytorch v1.0
Bug fix in networkx graph conversion.

0.1.2

First open release.

Basic graph APIs.
Basic message passing APIs.
Pytorch backend.
MXNet backend.
Optimization using SPMV.
Model examples w/ Pytorch:
- GCN
- GAT
- JTNN
- DGMG
- Capsule
- LGNN
- RGCN
- Transformer
- TreeLSTM
Model examples w/ MXNet:
- GCN
- GAT
- RGCN
- SSE