v4.0.0

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Changelog

• Give an :id to every member of the stack #130 - We've made formatting-stack substantially easier to configure, documenting so.
• eastwood.impl: use safer destructuring #131 - Eastwood bugfix

The :id requirement is a breaking change, because a user that provided a map-based custom member would have to add an :id to have things working again.

Release checklist (author)

• All PRs / relevant commits since the previous release are listed in this PR's description
• The new proposed version follows semver
• The build passes
• New features are (briefly) reflected in the README

Release checklist (reviewer)

• All PRs / relevant commits since the previous release are listed in this PR's description
• The new proposed version follows semver
• New features are (briefly) reflected in the README