Sentiment Analysis using Naive Bayes
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* Naive Bayes
* Add-1 smoothing
* 10-fold cross validation
* regular expression detecting negation words

Besides the regular method, the code also realized:
* Boolean Naive Bayes
* Naive Bayes with stop word
* Naive Bayes with negation features (not, never, n't)

Accuracy:
    * Regualr NB: 81.65%
    * Boolean NB: 73.85%
    * NB with stop word filterd: 81.10%
    * NB with negation features: 81.80%