[Release] DGL v0.3.1 Release

We have received many requests from our community for more GNN layers, models and examples. This is the time to respond. In this minor release, we enriched DGL with a ton of common GNN modules. We have also verified their correctness on some popular datasets so feel free to try them out. Another direction we are working on is to build more domain friendly packages based on DGL. As a first step, we released several pretrained GNN models for molecular property prediction and molecule generation (currently grouped under dgl.model_zoo namespace). We will continue explore this idea and release more domain specific models and packages.

This is a companion discussion topic for the original entry at https://www.dgl.ai/release/2019/08/28/release.html