[Fixes #376] Updates raylib-cpp to use raylib v6 API.

[execphantasmagoria]

This series of commits fixes some essential API changes. They are:

• Fixes references to raw bones, boneCount, bindPose to access through new ModelSkeleton struct.
• Updates outdated UpdateModelAnimationBones() to UpdateModelAnimaitonEx() or UpdateModelAnimaiton() wherever applicable and fixes data types.
• Renames frameCount and framePoses to keyframeCount and keyframePoses.
• Moves boneMatrices to Model instead of mesh.
• Removes redundant BoneInfo* bones in ModelAnimation.
• Updates UnloadModelAnimation() to UnloadModelAnimations() to use animCount. Set to 0 by default. Needs better implementation to unload all animations.

[RobLoach]

Most excellent!!! Brought it into that next branch over at #379 .