0.1.0 was never tagged, so the Unreleased section and the dated 0.1.0
entry describe the same, still unreleased, first version. Merge them
into one Added list ordered Bvh -> Bvh2d -> LineBvh/LineBvh2d.

Drop the Changed and Fixed sections: they tracked evolution within the
unreleased window (the Bvh2d rewrite, the build allocation work, LineBvh
becoming a wrapper) which is invisible to a first-time user. Facts worth
keeping moved into the Added bullets.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>