Use xbob.extension macros almost always

setup.py

src/xbob.blitz

xbob/io/externals.cpp

xbob/io/file.cpp

xbob/io/hdf5.cpp

xbob/io/include/xbob.io/api.h

xbob/io/main.cpp

xbob/io/videoreader.cpp

xbob/io/videowriter.cpp