Add support for line segments

[MartinSStewart]

This package fails to parse obj files that contain line segments (i.e. l 346 357). I'm guessing this is known since the limitations section in the readme says No free-form curves. If there are plans to extend this package then this feature would be useful for me.

Edit: I've implemented a version of it here that works well enough for my purposes but isn't good enough to release as a package https://github.com/MartinSStewart/elm-obj-loader. Still, it might be of use if you decide to work on this feature.

[declension]

Sorry, must have missed this somehow.

I've not really ended up using this, having ported it from @Zinggi's original. That said, if you'd like to make a PR from your fork that would be great :)

[MartinSStewart]

Hey declension! I've added line segment support but it's buggy and unfit for general use. If that changes then I'll make PR though.