Add SQA

## Adding a Dataset
- **Name:** SQA (Sequential Question Answering) by Microsoft. 
- **Description:** The SQA dataset was created to explore the task of answering sequences of inter-related questions on HTML tables. It has 6,066 sequences with 17,553 questions in total.
- **Paper:** https://www.microsoft.com/en-us/research/publication/search-based-neural-structured-learning-sequential-question-answering/
- **Data:** https://www.microsoft.com/en-us/download/details.aspx?id=54253
- **Motivation:** currently, the [Tapas](https://ai.googleblog.com/2020/04/using-neural-networks-to-find-answers.html) algorithm by Google AI is being added to the Transformers library (see https://github.com/huggingface/transformers/pull/8113). It would be great to use that model in combination with this dataset, on which it achieves SOTA results (average question accuracy of 0.71).

Note 1: this dataset actually consists of 2 types of files: 
1) TSV files, containing the questions, answer coordinates and answer texts (for training, dev and test)
2) a folder of csv files, which contain the actual tabular data

Note 2: if you download the dataset straight from the download link above, then you will see that the `answer_coordinates` and `answer_text` columns are string lists of string tuples and strings respectively, which is not ideal. It would be better to make them true Python lists of tuples and strings respectively (using `ast.literal_eval`), before uploading them to the HuggingFace hub.

Adding this would be great! Then we could possibly also add [WTQ (WikiTable Questions)](https://github.com/ppasupat/WikiTableQuestions) and [TabFact (Tabular Fact Checking)](https://github.com/wenhuchen/Table-Fact-Checking) on which TAPAS also achieves state-of-the-art results. Note that the TAPAS algorithm requires these datasets to first be converted into the SQA format.

Instructions to add a new dataset can be found [here](https://huggingface.co/docs/datasets/share_dataset.html).


I’ll take this one to test the workflow for the sprint next week cc @yjernite @lhoestq 

@thomwolf here's a slightly adapted version of the code from the [official Tapas repository](https://github.com/google-research/tapas/blob/master/tapas/utils/interaction_utils.py) that is used to turn the `answer_coordinates` and `answer_texts` columns into true Python lists of tuples/strings:

```
import pandas as pd
import ast

data = pd.read_csv("/content/sqa_data/random-split-1-dev.tsv", sep='\t')

def _parse_answer_coordinates(answer_coordinate_str):
  """Parses the answer_coordinates of a question.
  Args:
    answer_coordinate_str: A string representation of a Python list of tuple
      strings.
      For example: "['(1, 4)','(1, 3)', ...]"
  """

  try:
    answer_coordinates = []
    # make a list of strings
    coords = ast.literal_eval(answer_coordinate_str)
    # parse each string as a tuple
    for row_index, column_index in sorted(
        ast.literal_eval(coord) for coord in coords):
      answer_coordinates.append((row_index, column_index))
  except SyntaxError:
    raise ValueError('Unable to evaluate %s' % answer_coordinate_str)
  
  return answer_coordinates


def _parse_answer_text(answer_text):
  """Populates the answer_texts field of `answer` by parsing `answer_text`.
  Args:
    answer_text: A string representation of a Python list of strings.
      For example: "[u'test', u'hello', ...]"
  """
  try:
    answer = []
    for value in ast.literal_eval(answer_text):
      answer.append(value)
  except SyntaxError:
    raise ValueError('Unable to evaluate %s' % answer_text)

  return answer

data['answer_coordinates'] = data['answer_coordinates'].apply(lambda coords_str: _parse_answer_coordinates(coords_str))
data['answer_text'] = data['answer_text'].apply(lambda txt: _parse_answer_text(txt))
```

Here I'm using Pandas to read in one of the TSV files (the dev set). 



Closing since SQA was added in #1566