Textaugment

- now supports gensim >= 4

- now support fasttext models

- enhanced code to allow user to select top n words (synonyms/most similar words)

- added punctuation insertion

- Fixed minor issues

- Added support for Fasttext augmentation
- Added example notebook for Fasttext augmentation

- minor updates

- fix minor issues

- added [mixup](https://arxiv.org/abs/1710.09412) augmentation algorithm for NLP