The TfIdf Weighting scheme 

The code for tfidfweight.cc does not contain LOGCAL as Ill add it  and all relevant documentation for this scheme after working on the feedback.Have implemented all normalizations possible with the current statistics . The code is written in a way that is easy to add more normalizations after rewriting the backend for additional statistics.Have also tried to provide as extensive test coverage as I could .Please do let me know if any changes/additions/deletions are required.