Agree upon versioning strategy

[taylortom]

This one's been discussed a few times, but this needs to be decided & documented once and for all!

What we need:

• SIMPLE for devs to implement/adhere to
• Allow version clamping for peace of mind of testing/end-users
  • Should also apply to documentation so end-users/devs are able to look-up info with confidence

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Possible route:

• Versioning based on top-level first-party (i.e. adapt) deps (a minor version triggers a minor release etc.). Updates to 3rd party deps should only need patch releases but can be considered on a case-by-case basis
• Changelog can either link to the changelogs of each changed module, or include specifics for all changes. Don't mind which we go for here. Depending on whether we decide to log issues with individual modules in their relevant repos or log everything in this repo, automating this task could be tricky.