Version number

[duncandewhurst]

Related issues

Closes #145

Description

• Apply the version number agreed in #145
• Add a links field so that data can declare the version of the schema it is described by
• Add exceptions to tests
• Update schema URL

The schema URL will not resolve until the 020 tag is created and pushed. We'll only want to do that once we're ready to release version 0.2.0, but that isn't a blocker to merging this PR.

Merge checklist

• [x] Update the changelog (style guide)
• [x] Run ./manage.py pre-commit

If you added or removed a field:

• [x] Update the collapse option of the jsonschema directives for dataset, resource, hazard, exposure, vulnerability and loss on reference/schema.md

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[duncandewhurst]

@odscjames, @radix0000, heads up about this schema change that we discussed in yesterday's call. Also, reminder that OFDS uses the same links field to declare the version of the schema that describes a dataset, in case you need to borrow any code from its version of CoVE.

[duncandewhurst]

@odscjen please can you approve and merge. The only change since the approvals was to resolve merge conflicts in the changelog. To avoid these repeated review requests, I've updated the branch protection settings so that stale approvals are not dismissed when new commits are pushed.