Better sentiment analysis model

[ayush1999]

The current sentiment analysis model isn't very good, and needs to be changed (as discussed with @aviks ). Also, following the discussion in #83 , it'd be better to warn the user before skipping works not in vocabulary.

[aviks]

Benchmarking our existing model against standard datasets would be good place to start.

[ksteimel]

Sentiment analysis is a task that can be hard to transfer across different domains. Positive movie reviews may use different terminology when compared to positive video game reviews.

Should the emphasis be on making a generalizable model or making a decent model that you can easily augment with your own data in the target domain?

[aviks]

The latter, I would think. In any case, getting a good baseline+testcases would help in either case.

[ksteimel]

I have a repository where I benchmarked the current system.

The performance is very poor at 52% accuracy (only slightly above random chance).

This may be related to issue #129

[Shashi456]

@aviks In issue #129, you said the proposed change breaks the test cases, would you suggest fixing the model or writing a new one from scratch?