objLoader ignores smoothing groups declaration?

Unless I am completely mistaken, the `parseLine` function in `loadObj` does not take into account smoothing groups (declared in the obj format with `s [on|off|group_index]`).

Is this intentional (because maybe unnecessary in this context) or a current limitation of the `loadObj` parser?

Start by reading parseLine in loadObj and trace how OBJ declarations handle the s [on|off|group_index] forms. Determine whether smoothing groups are intentionally unsupported or a parser limitation; done means the intended treatment is explicitly resolved.

Written by the indexing model from the issue text.