core: Common: Add MAX3(a, b, c) macro.

Signed-off-by: Cyril Hrubis <metan@ucw.cz>
codegen: Propagate min, max to templating engine.

Signed-off-by: Cyril Hrubis <metan@ucw.cz>
core: Convert: Add experimental RGB -> CMYK.

BEWARE UNTESTED.

Signed-off-by: Cyril Hrubis <metan@ucw.cz>
tests: core: Cleanup BlitConv.

Signed-off-by: Cyril Hrubis <metan@ucw.cz>
core: Convert: Fix XXX -> XXXA conversion.

The alpha for blits from XXX -> XXXA wasn't filled propery. Was filled
with number of bytes rather than with the maximal value.

Signed-off-by: Cyril Hrubis <metan@ucw.cz>