Eliminate unnecessary branch in packed code
Use samples instead of bytes for packed function

For Avisynth all samples are one byte, so it's basically just a name
change, but after getting used to larger samples in Vapoursynth I find
it harder to visualize the functions' operation in terms of bytes.
Eliminate TurnsTile's depthMod member

Making this value available outside the constructor is a leftover from
versions before 0.3.0, when I did my scaling in GetFrame.
Move CLUTer field separation out of constructor