* Refactor datasets
* Update evaluators
* Update trainers
* Update main and MP-CNN model
* Add serialization util
* Fix bugs
* Refactoring for NCE to use new parent class
* Add TrecQA dataset and modularize MP-CNN infra
* Stylistic improvements
* Fix and warn about trec_eval path issue
* Update README for MP-CNN
* Update incorrect map/mrr
* MP-CNN: address code review comments
* Create common Castor pair Dataset class
* Move map and mrr computation to Castor utils
* Make map mrr utility trec_eval path more general