Add doc2dial dataset
It not always practical to use nested `Sequence`. If you have troubles with sequence you can use lists instead. 

For example
```python

features=datasets.Features(
    {
        "dial_id": datasets.Value("string"),
        "doc_id": datasets.Value("string"),
        "domain": datasets.Value("string"),
        "turns": [
            {
                "turn_id": datasets.Value("int32"),
                "role": datasets.Value("string"),
                "da": datasets.Value("string"),
                "reference": [
                    {
                        "keys" : datasets.Value("string"),
                        "values": datasets.Value("string"),   
                    }

                ],
                "utterance": datasets.Value("string"),
            }
        ],
    }
),
```

this way `turns` will be a list of dict, and the "reference" key of `turns` will be a list of dict as well No problem thanks for all your help getting this to the final stages! Added .gitignore, removed .lock and applied the changes you asked for.
### Doc2dial: A Goal-Oriented Document-Grounded Dialogue Dataset v0.9

Once complete this will add the [Doc2dial](https://doc2dial.github.io/data.html) dataset from the generic data sets list.