Highlighted changes:
* `jiant` 2.0 is a complete rewrite of `jiant`, built natively on [`transformers`](https://github.com/huggingface/transformers) and [`nlp`](https://github.com/huggingface/nlp)/[`datasets`](https://github.com/huggingface/datasets)
* Support for [50+ natural language understanding task](https://github.com/nyu-mll/jiant/blob/master/guides/tasks/supported_tasks.md), including the GLUE, SuperGLUE and XTREME benchmarks
* Support for BERT, RoBERTa, ALBERT, XLM-R, etc
* Includes data-downloading, tokenize-and-caching, training-and-evaluation code, and benchmark submission code for relevant tasks