Fix spine format
Cleaner matrix handling
Implement slots timeline
Remove `BoneData` structure
Fix only using the direct parent's transformations
Implement get_animation_duration
Revert "Remove `BoneData` structure"

This reverts commit 06c23c3b1d92e81a24e53b416268f2eee888f102.
Fix animations
Add `CalculationError` object
Add docs, fix warnings, minor tweak