Add reranking options and skeleton functions
Defined the re-ranker interface.
Adjust the re-ranker interface and finish the reranking process
Add the parameter to re-ranker inteface
Add batch re-ranking evaluation
Add batch re-ranking evaluation
Merge branch 'add_reranking_features' of https://github.com/yiweichen/Panda-information-retrieval-package into add_reranking_features
Add throwing exception to re-ranking interface
Add MMR process, using random similarity for now

TODO: comput similarity between documents.
Remove debug comments, sorry
Add setter and getter for totalWords variable
Fix the MAP bug
Add the batch GetDocTermStats
Update MMR re-ranking
fix bug with negative score
Add PortfolioReranker and Update BacthGetDocTermStats
Roll back unnecessary changes
fix
Add MAP switch in batch summary, false by default
Redesign the -r and -br arguments, using -m to specify the underlying model