Highlite:
 * use qualityLevel/zlib_buffer. No new variable is needed.
 * Change coding style to recursive fashion.
 * Change meaning of qualityLevel== 9 for easy calc zywrle_level:
     old:zywrle_level== 1
     new:disable ZYWRLE(same as ZRLE)
   so, we should not use this value for compatible reason.
 * Color mode handling isn't complete.
   I provided and checked 16 bit colors(RGB555,RGB565) and
   some color mode of 32 bit colors for little endian mode.
   we must make and check 24 bit colors and big endian mode.
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>