Add --md-anchors flag that emits HTML comment markers before each block
in Markdown output, allowing downstream tools to map excerpts back to
precise PDF locations.
Changes:
- Add markdown module with Anchor struct and parse_anchors() function
- Regex: <!-- pdftract: page=(\d+) block=(\d+) bbox=[([\d.,]+)] kind=(\w+) -->
- Add markdown_anchors: bool to ExtractionOptions
- Add --md-anchors CLI flag
- Implement block_to_markdown() and page_to_markdown() functions
- Add comprehensive documentation in docs/integrations/markdown-anchors.md
- 16 unit tests pass, including roundtrip test
Closes: pdftract-vk0gc
28c31ba0a1