Access to old and pre-release ontology variants

[jakebeal]

If we are generating ontology variants automatically (#116), it ought to be relatively straightforward to make them available via the ontology web service as well. The default URL should go to the current head, but tags and branches can be made accessible via the same sort of URL variants that GitHub uses for accessing tag and branch versions of materials.

[goksel]

Let's discuss this a bit more. I suggest versioning the ontology file more explicitly under a folder e.g. v2.0, v2.1 and so on.

[jakebeal]

Do you see a reason why the ontology version should not match the overall release version on the repository? I would expect that the major & minor version ought to always match the specification in any case, and we can potentially be much more free about incrementing patch versions.