Implement Categorized Product Sentiment Dataset [resolves #250]

[dafajon]

README.md

• Describe corpus and classes. Provide link to paper.

core.py

• Implement subset argument for loader and provide valid values in docstring.
• Selectively yield rows in iterator based on subset.
• Implement check for subset.
• Return all class values as integers and provide mappings.

__main__.py

• Validate both label columns.

test_categorized_product_sentiment

• Validate dataset loader for all subsets.

[husnusensoy]

What is the point of this dataset including 5600 instances ?