How to load diffuse, normal and specular texture

```
My object loads fine but it's by default yellow. I can set it to white using
'ModelColor' and I can load for example my diffuse texture by adding a
JSC3D.Texture. But how do I load them all? They are defined in my mtl file but
not loaded.
```

Original issue reported on code.google.com by `petersav...@variousskies.com` on 14 Mar 2014 at 2:21

Start by tracing how JSC3D.Texture is used and how the MTL file is read, since the issue says the diffuse, normal, and specular textures are defined there but not loaded. Determine whether the existing loading path can handle all three texture types, and consider the issue complete when an MTL-defined object loads each texture correctly.

Written by the indexing model from the issue text.