operators,

-   abs(diff(a,b))
+   max(a+b,255)
&   min(a,b)
|   max(a,b)

quant optimized some (not good enough, but better then before...)

Rev: src/modules/image/Makefile.src:1.10
Rev: src/modules/image/blit.c:1.8
Rev: src/modules/image/image.c:1.32
Rev: src/modules/image/image.h:1.15
Rev: src/modules/image/quant.c:1.16