Support for legal NLP datasets (EURLEX, ECtHR cases and EU-REG-IR)
Add support for two legal NLP datasets:

- EURLEX (https://www.aclweb.org/anthology/P19-1636/)
- ECtHR cases (https://arxiv.org/abs/2103.13084)
- EU-REG-IR (https://arxiv.org/abs/2101.10726)