Consider supporting Blender PBR material parameters

Apparently, the Blender folks recently took the liberty to just define new, additional parameters that can appear in MTL files: 
https://projects.blender.org/blender/blender/issues/101029. There is a nearly 1:1-correspondence of these parameters to the glTF PBR parameters. It could be worthwhile to look for these parameters, and provide a conversion to glTF PBR for them. 