* add gin model
* convert dataset.py to data_ont_the_fly way and put it into dgl.data module
* convert dataset.py to data_ont_the_fly way and put it into dgl.data module
python code checked
* modified document and reference TUDataset; checked python part and bypass cpp part due to error
* change tensor to numpy in dataset and transform in collate@Dataloader
* Change minor format issue
Change minor format issue
* moved logging; adjusted tqdm etc
kitaev-chen