Added document weight code to DocIdHandler
Changed test data to included multiple documents to check weights
Implemented BM25 Query Engine - Major structural changes to Query
* Made QueryEngine abstract class instead of function
* Moved index/lexicon reading into QueryEngine
* Added document weight calculation/writing/reading to DocIdHandler
* Added MinHeap class
* Added Timer class to make timing easier
* Fixed a couple of minor errors
* Added more documents to latimes_small for testing