Move extract_features, binarize_features, retrieve_images to tools/

diff --git a/examples/demo_binarize_features.cpp b/tools/binarize_features.cpp
similarity index 100%
rename from examples/demo_binarize_features.cpp
rename to tools/binarize_features.cpp

diff --git a/examples/demo_extract_features.cpp b/tools/extract_features.cpp
similarity index 100%
rename from examples/demo_extract_features.cpp
rename to tools/extract_features.cpp

diff --git a/examples/demo_retrieve_images.cpp b/tools/retrieve_images.cpp
similarity index 100%
rename from examples/demo_retrieve_images.cpp
rename to tools/retrieve_images.cpp