The specifications are not nearly stable enough to be publicized yet. In particular, there are several possibilities for file layout, compression, etc. and we have barely started toying with some of them, so any kind of spec we publish at this stage would be deprecated within a few weeks.
If you wish to follow the development of the reference implementation, you can find it here: https://github.com/Yoric/binjs-ref/ . It's very early and the format will change often as we
