* scribo/binarization/all.hh: Update includes.

	* scribo/binarization/internal/compute_local_threshold.hh,
	* scribo/binarization/internal/compute_sauvola_threshold.hh,
	* scribo/binarization/internal/first_pass_functor.hh,
	* scribo/binarization/internal/local_threshold_debug.hh,
	* scribo/binarization/internal/sauvola_debug.hh,
	* scribo/binarization/internal/sauvola_formula.hh,
	* scribo/binarization/sauvola.hh,
	* scribo/binarization/sauvola_ms.hh,
	* scribo/binarization/sauvola_threshold.hh,
	* scribo/binarization/sauvola_threshold_image.hh: Revamp code in
	order to share some parts with Niblack's algorithm.

	* scribo/binarization/internal/niblack_formula.hh,
	* scribo/binarization/niblack.hh,
	* scribo/binarization/niblack_threshold.hh: New.

	* src/binarization/Makefile.am
	* tests/binarization/Makefile.am: Add new targets.

	* src/binarization/niblack.cc: New tool.

	* tests/binarization/niblack.cc: New test.

	* tests/binarization/niblack.ref.pbm: New test data.