Serialization fixes

[bowald]

Summury

• Skips identity matrices for nodes during serialization.
• Skips empty ExtensionMap for materials during serialization
• Null values in ExtensionMap are serialized as empty object {} instead of being skipped (An extension witch contain null as value is KHR_materials_unlit )
• SerializeGltfParameter outputs Factor if numberArrays size is 1.
• Clang format tiny_gltf.h

To easier see my changes, see commit 6e96b12, first commit is only clang format

Discussion

Should default values (such as identity matrices) be skipped during serialization? Or is it up to the user of tinygltf to input correct data?

[syoyo]

Should default values (such as identity matrices) be skipped during serialization?

Yes, we can safely skip serializing default values where JSON schema defines it : https://github.com/KhronosGroup/glTF/blob/master/specification/2.0/schema/node.schema.json

[bowald]

Yes, we can safely skip serializing default values where JSON schema defines it

Good, I will keep adding checks against default values during serialization.

[syoyo]

@bowald Any updates?

[bowald]

@syoyo I'm sorry, been busy. will have some time to make fixes in the near coming weeks.