Bumps `@version` to 0.2.0 and assembles the three pending changelog
fragments into a `## [0.2.0]` section, deleting them in the same
commit per changelog.d/README.md.

A real minor: ADR-0006's datasets and expressions, the TruthTable
result matrix over them, and per-fragment fixture bundles all became
public surface since 0.1.1. All thirteen fragment entries carry over
verbatim under one `### Added` heading.

The tag, the GitHub release, and `mix hex.publish` are deliberately
not part of this commit.

Refs: sui-c0n