Improvements + a nice dithered image example on Amstrad

Here are our latest improvements about Image-To-Amstrad converter:

(v1.228)

• [+++] Detects if "not enough colors for palette" => complete with dominant colors. Especially useful in -mode0
• [New] Perform complete histogram on colors of the original image to suggest default palette (-palAuto)       (Use -log-palauto2 to print verbose information about automated palette and color affinity.)
• [New] Detect light levels complete histogram to suggest default values for grayscale min_light and max_light      (Use -log-grayscale2 to print verbose information about light levels histogram.)
• [Fix] Fixed a conversion result when -affinity is used without -dither
• [Fix] Fixed a conversion result when -affinity is used combined with -grad