Release v0.3.2

- Comprehensive Javadoc improvements across all public types: package-level
  descriptions with quick-start code examples, encoding/decoding lifecycle
  guides, detailed per-method parameter and return documentation, memory-contract
  explanations (Arena ownership, libvpx buffer lifetime), thread-safety notes,
  and cross-references between related classes.
- New package-info.java files for org.seuffert.panvpx, core, vp8, and vp9
  packages, each containing an overview, usage example, and links to key types.