Issues to Look back to:

• Provide user with Bigram Term iterator and unigram Term iterator or not.Will it help to have a bigram term iterator.

• Document length stored in term-list and post-list table need to be revised and set accordingly.

• get_stats function in postingiterator and postlist is currently inefficient as it access all four statistics even if only one statistics is required.Maybe make the function parametric and be able to specify which all things statistics you need.