Drafting an XML format

I'm a bit suprised at myself, just last year arguing that XML was being over-used, now attempting to implement an optimized XML format for Soya.

The job isn't simple, since I'm working on soya.Mesh at the same time and these are intricatly linked. On one side we have Blender/etc which already have neighbors, normals, etc computed. On the other we want the data to be user-editable in it's text format. And lastly, Soya needs to be able to load and save this format more efficiently than Cerializer.

Blender importers/exporters should be able to drop data into this format without using Soya. It should survive extension for future Soya features and be permissable both in a file by itself and bundled with other data.