Describe the Bug

If you were to click the v0.3 and v1.0 links on this table on the readme, https://github.com/cloudevents/sdk-javascript#supported-specification-features, they return a 404 since they don't link anywhere.

We could/should probably link out to the appropriate section in the spec repo.

I did notice however, that the spec repo only has a master and v1.0 branches, https://github.com/cloudevents/spec/branches/all so i'm not sure where to get the v0.3 spec links