Missing shadows

[furrtek]

Particularly noticeable and annoying in TMNT's sewer stage 3.
Must be something with the k051962 or layer mixing.

[jotego]

See #18

[paulb-nl]

This is the fix for shadows: paulb-nl@08cc854

Shadow buffer Q output was registered so output was 1 cycle too late for AK196/AK154 latch.

Shadows are working but the brightness needs tweaking. I think they are too dark.