Cli for exploring different datasets

[abhinavkashyap]

There are different classification datasets that are part of the repo now. A cli to explore the different datasets would be a nice feature to have. Get stats is already part of the interface.

The cli should

1. Ask which dataset to explore
2. The user should be able to see basic vocab stats of the dataset (Number of distinct words. Most popular words)
3. Other information about the dataset, like number of training examples, validation examples, the max length of instances