Add StackOverflow StackSample dataset
NONE
@lhoestq Thanks for the review and suggestions! I've added your comments and pushed the changes. I'm having issues with the dummy data still. When I run the dummy data test

```bash
RUN_SLOW=1 pytest tests/test_dataset_common.py::LocalDatasetTest::test_load_dataset_all_configs_so_stacksample
```
I get this error: 

```
___________________________________________ LocalDatasetTest.test_load_dataset_all_configs_so_stacksample ____________________________________________

self = <tests.test_dataset_common.LocalDatasetTest testMethod=test_load_dataset_all_configs_so_stacksample>, dataset_name = 'so_stacksample'

    @slow
    def test_load_dataset_all_configs(self, dataset_name):
        configs = self.dataset_tester.load_all_configs(dataset_name, is_local=True)
>       self.dataset_tester.check_load_dataset(dataset_name, configs, is_local=True)

tests/test_dataset_common.py:237: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
tests/test_dataset_common.py:198: in check_load_dataset
    self.parent.assertTrue(len(dataset[split]) > 0)
E   AssertionError: False is not true

FAILED tests/test_dataset_common.py::LocalDatasetTest::test_load_dataset_all_configs_so_stacksample - AssertionError: False is not true
```

I tried formatting the data similar to other datasets, but I think I don't have my csv's in the zip folder with the proper name. I also ran the command that's supposed to outline the exact steps I need to perform to get them into the correct format, but I followed them and they don't seem to be working still :/. Any help would be greatly appreciated!

2020-12-12T14:30:48Z
https://github.com/huggingface/datasets/pull/1356#issuecomment-743764333
https://api.github.com/repos/huggingface/datasets/issues/1356
MDEyOklzc3VlQ29tbWVudDc0Mzc2NDMzMw==
https://api.github.com/repos/huggingface/datasets/issues/comments/743764333/reactions
2020-12-12T14:31:40Z
https://api.github.com/repos/huggingface/datasets/issues/comments/743764333
https://avatars.githubusercontent.com/u/7613470?v=4
https://api.github.com/users/ncoop57/events{/privacy}
https://api.github.com/users/ncoop57/followers
https://api.github.com/users/ncoop57/following{/other_user}
https://api.github.com/users/ncoop57/gists{/gist_id}
https://github.com/ncoop57
ncoop57
MDQ6VXNlcjc2MTM0NzA=
https://api.github.com/users/ncoop57/orgs
https://api.github.com/users/ncoop57/received_events
https://api.github.com/users/ncoop57/repos
https://api.github.com/users/ncoop57/starred{/owner}{/repo}
https://api.github.com/users/ncoop57/subscriptions
User
https://api.github.com/users/ncoop57
public
MEMBER
Ok I found the issue with the dummy data.
It's currently failing because it's not generating a single example using the dummy csv file.
That's because there's only only line in the dummy csv file, and this line is skipped using the `next()` call used to ignore the headers of the csv.

To fix the dummy data you must add headers to the dummy csv files.
2020-12-14T17:37:09Z
https://github.com/huggingface/datasets/pull/1356#issuecomment-744597062
https://api.github.com/repos/huggingface/datasets/issues/1356
MDEyOklzc3VlQ29tbWVudDc0NDU5NzA2Mg==
https://api.github.com/repos/huggingface/datasets/issues/comments/744597062/reactions
2020-12-14T17:37:09Z
https://api.github.com/repos/huggingface/datasets/issues/comments/744597062
https://avatars.githubusercontent.com/u/42851186?v=4
https://api.github.com/users/lhoestq/events{/privacy}
https://api.github.com/users/lhoestq/followers
https://api.github.com/users/lhoestq/following{/other_user}
https://api.github.com/users/lhoestq/gists{/gist_id}
https://github.com/lhoestq
lhoestq
MDQ6VXNlcjQyODUxMTg2
https://api.github.com/users/lhoestq/orgs
https://api.github.com/users/lhoestq/received_events
https://api.github.com/users/lhoestq/repos
https://api.github.com/users/lhoestq/starred{/owner}{/repo}
https://api.github.com/users/lhoestq/subscriptions
User
https://api.github.com/users/lhoestq
public
MEMBER
Also can you make sure that all the original CSV files have headers ? i.e. check that their first line is just the column names
2020-12-14T17:37:44Z
https://github.com/huggingface/datasets/pull/1356#issuecomment-744597370
https://api.github.com/repos/huggingface/datasets/issues/1356
MDEyOklzc3VlQ29tbWVudDc0NDU5NzM3MA==
https://api.github.com/repos/huggingface/datasets/issues/comments/744597370/reactions
2020-12-14T17:38:05Z
https://api.github.com/repos/huggingface/datasets/issues/comments/744597370
https://avatars.githubusercontent.com/u/42851186?v=4
https://api.github.com/users/lhoestq/events{/privacy}
https://api.github.com/users/lhoestq/followers
https://api.github.com/users/lhoestq/following{/other_user}
https://api.github.com/users/lhoestq/gists{/gist_id}
https://github.com/lhoestq
lhoestq
MDQ6VXNlcjQyODUxMTg2
https://api.github.com/users/lhoestq/orgs
https://api.github.com/users/lhoestq/received_events
https://api.github.com/users/lhoestq/repos
https://api.github.com/users/lhoestq/starred{/owner}{/repo}
https://api.github.com/users/lhoestq/subscriptions
User
https://api.github.com/users/lhoestq
public
NONE
> Ok I found the issue with the dummy data.
> It's currently failing because it's not generating a single example using the dummy csv file.
> That's because there's only only line in the dummy csv file, and this line is skipped using the `next()` call used to ignore the headers of the csv.
> 
> To fix the dummy data you must add headers to the dummy csv files.

Oh man, I bamboozled myself! Thank you @lhoestq for catching that! I've updated the dummy csv's to include headers and also confirmed that they all have headers, so I am not throwing away any information with that `next()` call. When I run the test locally for the dummy data it passes, so hopefully it is good to go :D
2020-12-21T01:25:10Z
https://github.com/huggingface/datasets/pull/1356#issuecomment-748708602
https://api.github.com/repos/huggingface/datasets/issues/1356
MDEyOklzc3VlQ29tbWVudDc0ODcwODYwMg==
https://api.github.com/repos/huggingface/datasets/issues/comments/748708602/reactions
2020-12-21T01:25:33Z
https://api.github.com/repos/huggingface/datasets/issues/comments/748708602
https://avatars.githubusercontent.com/u/7613470?v=4
https://api.github.com/users/ncoop57/events{/privacy}
https://api.github.com/users/ncoop57/followers
https://api.github.com/users/ncoop57/following{/other_user}
https://api.github.com/users/ncoop57/gists{/gist_id}
https://github.com/ncoop57
ncoop57
MDQ6VXNlcjc2MTM0NzA=
https://api.github.com/users/ncoop57/orgs
https://api.github.com/users/ncoop57/received_events
https://api.github.com/users/ncoop57/repos
https://api.github.com/users/ncoop57/starred{/owner}{/repo}
https://api.github.com/users/ncoop57/subscriptions
User
https://api.github.com/users/ncoop57
public
MEMBER
merging since the Ci is fixed on master
2020-12-21T14:48:17Z
https://github.com/huggingface/datasets/pull/1356#issuecomment-749010874
https://api.github.com/repos/huggingface/datasets/issues/1356
MDEyOklzc3VlQ29tbWVudDc0OTAxMDg3NA==
https://api.github.com/repos/huggingface/datasets/issues/comments/749010874/reactions
2020-12-21T14:48:17Z
https://api.github.com/repos/huggingface/datasets/issues/comments/749010874
https://avatars.githubusercontent.com/u/42851186?v=4
https://api.github.com/users/lhoestq/events{/privacy}
https://api.github.com/users/lhoestq/followers
https://api.github.com/users/lhoestq/following{/other_user}
https://api.github.com/users/lhoestq/gists{/gist_id}
https://github.com/lhoestq
lhoestq
MDQ6VXNlcjQyODUxMTg2
https://api.github.com/users/lhoestq/orgs
https://api.github.com/users/lhoestq/received_events
https://api.github.com/users/lhoestq/repos
https://api.github.com/users/lhoestq/starred{/owner}{/repo}
https://api.github.com/users/lhoestq/subscriptions
User
https://api.github.com/users/lhoestq
public
This PR adds the StackOverflow StackSample dataset from Kaggle: https://www.kaggle.com/stackoverflow/stacksample

Ran through all of the steps. However, since my dataset requires manually downloading the data, I was unable to run the pytest on the real dataset (the dummy data pytest passed).