Feat
- add fetcher for validation predictions
- add fetcher for example predictions
- add fetcher for live data
- add fetcher for test data
- add fetcher for tournament data
- add targets attribute
- remove na_value argument
- use original data types
- return metadata as separate attributes
BREAKING CHANGE
- remove support for NaN value replacement in fetchers.
- don't convert `era`s to int.
- replace the dataset's `info` attribute by `id`, `era`
and `data_type` attributes.