Set version 0.1.2-SNAPSHOT in extension.json and use @since 0.1.2 for all patches.

When bumping version, set 0.1.2 in extension.json and update CHANGES.md from 0.1.2-SNAPSHOT to 0.1.2.
If version bump was greater than originally planned (e.g. from 0.1.2 to 0.2.0), update @since-tags in affected patches?

Create new paragraph for next future -SNAPSHOT version in CHANGES.md