VocabLib/include/VocabTree.h
* In struct VocabTreeParams, added direct index level as attribute.
* In class VocabTree, added attributes for implementing direct index
level.
* In method VocabTree::quantize, added parameter that allows to retrieve
the best node at a given level.
* In class VocabTree, added method for adding a feature to the direct
index.
* In VocabTree constructor, initializing direct index level attribute
using attribute in VocabTreeParams.
* In method VocabTree::addImageToDatabase, initializing direct index
entries.