[TODO] Partial update feature for glTF model

[syoyo]

It would be nice if we have a feature to partially update(or patching) glTF model, for example overwrite material/animation parameters using another glTF(or JSON) file which only contain material/animation parameters onto loaded glTF model.

There was a discussion about referencing feature in glTF community

KhronosGroup/glTF#37

But consensus was not obtained among the community to making it glTF standard.

For a while, TinyGLTF could implement referencing or patching feature as an extension.

[syoyo]

At least glTF spec itself allows reading glTF file only contains material field.

KhronosGroup/glTF#1420