Update CHANGELOG.md to use inline links

[chrismytton]

Problem

Each time we add a version to CHANGELOG.md we need to also remember to add a line at the very bottom of the file to make the reference links work.

Proposed solution

Move the links so they're inline, which will make it more obvious that they need updating when people copy/paste a new version.

Acceptance criteria

The list of reference links at the bottom of CHANGELOG.md should go away and be replaced by inline links.