Wongnai - Thai reviews dataset
Thank you for contributing a Thai dataset, @mapmeld ! I'm super hyped. 
One comment I may add is that wongnai-corpus has two datasets: review classification (this) and word tokenization (https://github.com/wongnai/wongnai-corpus/blob/master/search/labeled_queries_by_judges.txt).
Would it be possible for you to rename this one something along the line of `wongnai-reviews` so that when/if we include the word tokenization dataset, we will know which is which.

This helps solve my check_code_quality issue.
```
make style
black --line-length 119 --target-version py36 datasets/wongnai
flake8 datasets/wongnai
isort datasets/wongnai/wongnai.py
``` @cstorm125 thanks! following your suggestions on formatting and on naming the dataset

I am writing a blog post about Thai NLP and transformers (example: mBERT does 1-2 character tokens instead of doing word segmentation), started adding this dataset to use as an example, and then saw you were adding other datasets. Great work! And if you know any Thai BERT models beyond https://github.com/ThAIKeras/bert we should maybe talk over email!
40,000 reviews, previously released on GitHub ( https://github.com/wongnai/wongnai-corpus ) with an LGPL license, and on a closed Kaggle competition ( https://www.kaggle.com/c/wongnai-challenge-review-rating-prediction/ )