adds function to create BoF
Merge branch 'BoF_InvertedIndex'
adds comment for packages required but not installed from PyPI
Merge branch 'master' into BoF_InvertedIndex
separate index creation from bof()
wrap pyflann from API
BoF => BoFMaker
adds interface to save/load index of visual words
adds Redis-backend invert index
Merge branch 'BoF_InvertedIndex'