REVIEWED: Reorganized structures for a clearer distinction between "skeleton", "skin" and "skinning" data
ADDED: New structures: `ModelSkeleton`, `ModelAnimPose` (alias `Transform*`)
ADDED: Runtime data `currentPose` and `boneMatrices` to `Model` structure
ADDED: Support animation frames-blending, for timing control
ADDED: Support animations blending, between two animations
REVIEWED: All models animation loading functions
ADDED: `UpdateModelAnimationEx()` for two animations blending
REMOVED: `UpdateModelAnimationBones*()`, simplified API
REVIEWED: Shader attributes/uniforms names for animations, for consistency
REVIEWED: Multiple tweaks on animations loading for consistency between formats
ADDED: example: `models_animation_timing`
ADDED: example: `models_animation_blending`
REVIEWED: example: `models_animation_gpu_skinning`
REVIEWED: example: `models_animation_blend_custom`
REVIEWED: All animated models loading examples
