Adopt a Versioning Policy #5
From https://github.com/openraster/ora-project/issues/5
OpenRaster's specification basically has one already: we use Semantic Versioning there.
It's a sensible scheme, and it should be good enough for all project outputs, I think. Let's write a proper document saying what we do here in ora-project, and maybe add a note on how we'll map versions to github tags for the spec.