v0.4.0

• New format version (3)
• API breaking changes
  • All metadata types (e.g. ChunkMeta) now live in the pco::metadata:: module.
  • Metadata and ChunkCompressor types are no longer generic to latent type. Instead they contain dynamically-typed values, leveraging the dtype_dispatch crate.
  • Renamed NumberLike => Number.
  • Delta encoding is now configured via DeltaSpec enum of an Option<usize>, and similarly ChunkMeta contains a DeltaEncoding enum.
• API additions
  • Added simple_compress_into function.
  • Added a Lookback delta encoding that improves compression ratio on some types of data.
• Improvements
  • Improved bin optimization speed on Windows slightly.
  • Improved FloatQuant auto mode heuristics, improving the size/speed tradeoff.
  • Reduced binary size via fewer unnecessary specializations.
• Degradations
  • Automatic detection of the new Lookback delta encoding is fairly slow, often increasing compression time ~10%. We're likely to try ameliorating this in future releases.