Add scripts to color-reduce pictures with constraints

Scripts for various Thomson machines, Oric and ZX. All the hard work of
Samuel Devulder, with extensive research on color palette reduction
algorithms, lots of testing, research and debugging.

Thanks a lot!

share/grafx2/scripts/samples_2.4/picture/thomson/none_mo5.lua

@@ -0,0 +1,27 @@
+-- ostro_mo5.lua : converts a color image into a 
+-- MO5 image (16 fixed colors with color clash) 
+-- using Ostromoukhov's error diffusion algorithm.
+--
+-- Version: 02-jan-2017
+--
+-- Copyright 2016-2017 by Samuel Devulder
+--
+-- This program is free software; you can redistribute
+-- it and/or modify it under the terms of the GNU
+-- General Public License as published by the Free
+-- Software Foundation; version 2 of the License.
+-- See <http://www.gnu.org/licenses/>
+
+run('lib/ostromoukhov.lua')
+
+local dith=OstroDither:new()
+local tmp=dith.setLevelsFromPalette
+dith.setLevelsFromPalette = function(self)
+	tmp(self)
+	self.attenuation=0
+end
+dith:dither40cols(function(w,h,getLinearPixel)
+	local pal={}
+	for i=0,15 do pal[i+1] = thomson.palette(i) end
+	return pal
+end)