(word-embedding models) https://stackoverflow.com/questions/45310409/using-a-word2vec-model-pre-trained-on-wikipedia
https://stackoverflow.com/questions/27470670/how-to-use-gensim-doc2vec-with-pre-trained-word-vectors
https://radimrehurek.com/gensim/models/doc2vec.html
(ipynb usage example) https://github.com/RaRe-Technologies/gensim/blob/develop/docs/notebooks/doc2vec-lee.ipynb
https://stackoverflow.com/questions/42781292/doc2vec-get-most-similar-documents
http://web.stanford.edu/class/cs224n/
https://stats.stackexchange.com/questions/277014/what-parameters-to-optimize-in-knn (for KNN optimization) https://www.pyimagesearch.com/2016/08/15/how-to-tune-hyperparameters-with-python-and-scikit-learn/