GitLab

* fix gat residual bug

* fix the residual addition; output heads; add some shape notations;

* minor

* fix the output head average

* add requests package in requirement

* update example readme

* mx example readme

* add results in readme

* mx rgcn readme

* update readme.

* update readme

1. Update `examples/pytorch/gcn` and `python/dgl/nn/pytorch` based on the latest APIs
2. Add full support for dropout in `examples/pytorch/gcn` and `python/dgl/nn/pytorch`
3. Rename `GCN` class in `python/dgl/nn/pytorch` to be `GraphConvolutionLayer` class
4. Make node field an argument that can be configured by users in GraphConvolutionLayer

Note that adjacency normalization has not been supported yet in the examples. 

* synthetic dataset

* some fix

* gcn readme