Enable GPU skinning in the default build.

Have the model animation update functions check the current shader to see if they are going to do GPU skinning or not.
Lazy load the CPU animation buffers so they don't get allocated if the user is doing GPU skinning.
This change allows both GPU and CPU skinning in the same program.

src/raylib.h

@@ -1649,6 +1649,8 @@ RLAPI void SetModelMeshMaterial(Model *model, int meshId, int materialId);
 RLAPI ModelAnimation *LoadModelAnimations(const char *fileName, int *animCount);            // Load model animations from file
 RLAPI void UpdateModelAnimation(Model model, ModelAnimation anim, float frame);             // Update model animation pose (vertex buffers and bone matrices)
 RLAPI void UpdateModelAnimationEx(Model model, ModelAnimation animA, float frameA, ModelAnimation animB, float frameB, float blend); // Update model animation pose, blending two animations
+RLAPI void UpdateModelAnimationBones(Model model, ModelAnimation anim, float frame);        // Update model animation pose (bones only)
+RLAPI void UpdateModelAnimationBonesEx(Model model, ModelAnimation animA, float frameA, ModelAnimation animB, float frameB, float blend); // Update model animation bones to pose, blending two animations
 RLAPI void UnloadModelAnimations(ModelAnimation *animations, int animCount);                // Unload animation array data
 RLAPI bool IsModelAnimationValid(Model model, ModelAnimation anim);                         // Check model animation skeleton match