ZENGINE: Allow a angle buffer zone on *both* sides of the actual angle
ZENGINE: Round to int *after* converting to degrees
ZENGINE: Fix the quadrant numbers in angle calculations

Because y increases as you go down, not up
ZENGINE: Implement avi frame seeking
ZENGINE: Add support for animation 'mirroring'

If an animation is 'mirrored', it doesn't have B-frames, only I-frames. However the animations are built
so the last half of the animation is the reverse of the first half
ZENGINE: Remove RlfAnimation::getPreviousFrame()

I realized that RlfAnimations don't use B-frames, therefore, can not easily go backwards.
ZENGINE: Fix: Signal a cursor change
ZENGINE: Fix: Store what type of animation file is used
squash avi support
ZENGINE: Fix: Change infndef to correct constant
ZENGINE: Add LeverControl to scr file parsing
ZENGINE: Increase background rotation speed

This could probably still go higher. The DOS version is *very* sensitive, too sensitive.
But this is still a bit slow.