v0.4.0

Added

• Generalized XMP property writer: arbitrary group:property keys with value
  shapes (scalar, rdf:Alt x-default, rdf:Bag, rdf:Seq), per-namespace
  xmlns declaration, upsert-or-replace semantics, and fresh-packet fallback
  when a container has no XMP.
• P0 descriptive tags on all write containers: XMP-dc:Subject (keywords Bag,
  replace-not-append), XMP-dc:Title, XMP-dc:Description
  (Alt/x-default), XMP-xmp:MetadataDate.
• XMP embedding per container: PNG (iTXt, uncompressed, keyword
  XML:com.adobe.xmp), WebP (XMP RIFF chunk + VP8X flag), plain TIFF
  (IFD0 XMP/XMLPacket tag 0x02BC) — previously EXIF-only.
• IPTC IIM writer for JPEG APP13: repeatable Keywords (record 2, dataset 25)
  plus CodedCharacterSet (record 1, dataset 90) = UTF-8; merges into an
  existing Photoshop IRB, replacing only the 8BIM 0x0404 block.
• ExifTool.writeSidecar(): Lightroom-readable .xmp sidecar for RAW/DNG
  pickup, with read-merge of unknown properties and idempotent re-runs.
• ExifToolCore.writeBytes (in-memory path) supports all of the above.

Changed

• TIFF writing restricted to plain TIFF: camera RAW (CR2, NEF, ARW, …) and
  files with SubIFDs (DNG raw data, previews, tiles) throw
  UnsupportedFormatError instead of risking corruption — use the sidecar
  mode for those.

Fixed

• TIFF writer used a typo'd XMP tag id (0xBC01); the real XMP/XMLPacket tag
  is 0x02BC.
• Big-endian TIFF version check read bytes 2/3 swapped, rejecting valid
  big-endian TIFF files.

Known limitation

• Adding EXIF entries to a JPEG can shift value areas in the rebuilt EXIF
  block, breaking MakerNotes whose internal offsets are absolute from the
  TIFF header (e.g. Olympus). XMP/IPTC-only writes never touch the EXIF
  block. Reference exiftool fixes this with per-maker offset logic.