base_question_pos_tags and base_question_entity_tags

[YerongLi]

Hi, I am wondering how you generate base_question_pos_tags and base_question_entity_tags ?

- `base_question`: Base/original question
- `base_question_pos_tags`: Base question where each word is replaced by its POS tag,
- `base_question_entity_tags`: Base question where each word is replaced by a tag which indicates if  they are an named entity.
- `base_question_letter_cases`: Base question where each word is replaced by "UP" if it's an uppercase word and "LOW" if it's a   lowercase one.