Added lookup() method to Vocabulary

While quantize() returns the input data quantized to the vocabulary words,
lookup() return the indices of the corresponding words.
Documentation
WIP Added BagOfWords template extractor
fixup wrong template in callbacks with crp
Vocabulary factory method with template on Extractor
fixup bow
Using BagOfWord extractor and deleted old callbacks_hog
Using Vocabulary& instead of Vocabulary*
Fixed BagOfWord::extract() function

Need to arma::hist passing a arma::linspace rather than num of bins.
fixup hsv
TEMP Added Armadillo usage tests
TEMP More Armadillo Usage
Removed obsolete ported functions

Moved the remaining required ones to hsv_aux.hpp