a few changes for CImg.v1.5.6 (on crop, display, distorsion, only yet !)
modified:   VERSION_CIMG: CImg version checkout (CImg.v1.5.6).
modified:   crop/_info.crop.txt: small changes.
modified:   display/CImg.display.cpp: changes for get_shared_line to get_shared_row.
modified:   distorsion/CImg.warping.cpp: changes for get_shared_line to get_shared_row and get_shared_plane to get_shared_slice.
modified:   distorsion/Makefile: CImg version v1.5.6 .
modified:   distorsion/_info.txt: add compilation line.
small changes for CImg.v1.5.6 compliance.
modified:   fourier/_info.fourier_transform.txt: small change.
modified:   hough/_info.hough_transform.txt: small change.
modified:   label/labeling.cpp: change labeling function name to comply with CImg.v1.5.6 .
changes for CImg.v1.5.6 are compiling.
odified:   object_displacement/object_displacement_loop.cpp: function change.