3D models support for spritexoffset, spriteyoffset, spritexscale, spriteyscale, parity with sprite rollangle

"Parity with sprite rollangle" means models rotate relative to the camera instead of on a specific axis.

rotaxis has been deprecated in sprite info.

Some of the code in this branch was built upon a change made in Ring Racers that sets the pitch and roll fields of an object to match the standingslope. The object would then tilt to match the slope this way. (Models can even rotate in 3 dimensions!)

I've disabled the pitch/roll code for now but if this should be a base game feature in SRB2 as well, 78a52ce9 can be easily reverted. Additionally, the pivot point for some sprites, such as players, may need to be updated to complete this effect. There's not an easy way to do this right now except by setting it for every frame of a sprite individually. Lach suggested using the sprite offsets as the pivot point.