adding TabFact dataset
Adding TabFact: A Large-scale Dataset for Table-based Fact Verification.

https://github.com/wenhuchen/Table-Fact-Checking

- The tables are stored as individual csv files, so need to download 16,573 🤯  csv files. As a result the `datasets_infos.json` file is huge (6.62 MB).
- Original dataset has nested structure where, where table is one example and each table has multiple statements,
flattening the structure here so that each statement is one example.
FYI you guys are on GitHub's homepage 😍

<img width="1589" alt="Screenshot 2020-12-09 at 12 34 28" src="https://user-images.githubusercontent.com/326577/101624883-a0ecc700-39e8-11eb-8a97-11af0d036536.png">
 Yeayy 😍 🔥