Ability to read .3DS biinary files

[runette]

So, I needed the ability to read .3DS files and extract meshes and since we are exclusively using g3 to read and manipulate meshes I decided to do it properly and create a reader for .3ds files in g3 ( called DS3Reader for obvious reasons).

I have added this as a PR in case it is of interest.

At the moment - it is read-only and only extracts the mesh, not the materials.

see #150