Implement active versioning / version bumping of the specification

[alilleybrinker]

Right now, the specification is under heavy editing, and is perpetually at version 0.1. That said, it may be better to actually handle bumping the version of the spec when changes are made to it. Given that it's pre-1.0, any changes to the spec would constitute a minor version bump. This at least lets us be more concrete about referring to changes in the spec as it continues to evolve.

I'd also argue that changes to any of the annexes be considered as a change to the overall spec, necessitating a version bump. Ideally, new versions would also be tagged.