Fixing bug, having smaller count array.

countarray stores light count for caculating average, but it doesn't
have enough slots to store all light value. It's within 0 to 255.
Levels of lights are 256! (not 255).
It must have 256 slots to store count all light levels.
Merge pull request #24 from lanterrt/patch-1

Fixing bug, having smaller count array.