Merge pull request #7 from relentlesscoder/feature-QL(Language_Model)

Feature ql(language model)
Implemented the linear ranker

1. Implemented the linear ranker naively for now.
2. Sort scored document in the handler instead of in the ranker.
Merge pull request #8 from relentlesscoder/feature-linear_ranker

Implemented the linear ranker
Merge pull request #9 from relentlesscoder/develop

Develop