first attempt to add support for geom but I don't like much the design

vertex descriptions shouldn't be like that. I don't like the current
create_vertex_descriptions, I need to dynamically allocate as many as I
need to fit vertices, indices, normals and tangents.

I am also not sure if geometry should store all the vertices or just
information about which ones are used. The data will be send later. When
I create the renderer, the pipelines etc I only need the *description*.

So to be fixed.