[WIP] MongoDB coll <- TSV/CSV/JSON 

This PR handles ingest of TSV/CSV/JSON files into Mongo DB collections
`into.dispatch(Collection, DataDescriptor)` fill find the following function:

```Python
def into(coll, dd, chunksize=1024, **kwargs):
    return into(coll, iter(dd), chunksize=chunksize, schema=dd.schema)
```

That's the one that I think we want to run.