add PIB dataset
Hi, 

I am unable to get success in these tests. Can someone help me by pointing out possible errors?

Thanks Hi ! you can read the tests by logging in to circleci.

Anyway for information here are the errors : 
```
datasets/pib/pib.py:19:1: F401 'csv' imported but unused
datasets/pib/pib.py:20:1: F401 'json' imported but unused
datasets/pib/pib.py:36:84: W291 trailing whitespace
```
and 
```
FAILED tests/test_file_encoding.py::TestFileEncoding::test_no_encoding_on_file_open
```

To fix the `test_no_encoding_on_file_open` you just have to specify an encoding while opening a text file. For example `encoding="utf-8"`
 All suggested changes are done. Nice ! can you re-generate the dataset_infos.json file to take into account the feature type change ?
```
datasets-cli test ./datasets/pib --save_infos --all_configs --ignore_verifications
```
And also format your code ?
```
make style
```
This pull request will add PIB dataset.