This initial implementation emulates the way RMVX splits
the sprite into "chunks" of about 8 pixels, which it then
scrolls left/right on a vertical sine wave. It even
replicates the weird behavior when wave_amp < 0, namely
"shrinking" the src_rect horizontally.
As with bush_opacity, this effect in combination with
rotation will render differently from RMVX.
Previously, wrapped instances of mkxp core classes were
stored as RData ivars inside the actual object. This turned
out to be pointless as RData objects themselves are perfectly
valid objects that can carry ivars and have parent classes.
Therefore, the RData objects are now exposed directly to
the user scripts, effectively halving the amount of object
allocations.