Add WMF to SVG Conversion and Image Inclusion in Markdown Output

[laura-dietz]

This PR introduces two key enhancements to pptx2md, improving its robustness and extending support for vector graphics.

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🔧 Summary of Changes

1. WMF Image Support and SVG Conversion

• Adds support for extracting .wmf images from PowerPoint files.

• Automatically converts .wmf to .svg using inkscape CLI:

  inkscape input.wmf --export-type=svg --export-filename=output.svg --export-plain-svg

• References the .svg in the Markdown output for inclusion in rendered output.

2. Bug Fix: Shape Sorting Crash

• Fixes a bug in parser.py where ungrouped shapes could lack top or left attributes.

• This previously caused attrgetter('top', 'left') to crash conversion on some slides.

• Now uses:

  shapes = [sp for sp in ungroup_shapes(...) if getattr(sp, "top", None) is not None]
  shapes.sort(key=attrgetter('top', 'left'))

• Prevents hard crashes and logs a warning when a malformed shape is encountered.

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✅ Behavior Improvements

• Gracefully skips and logs invalid shapes instead of crashing.
• Enables full extraction and rendering of .wmf-based diagrams, equations, and flowcharts — often used in academic slides.

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🧱 Dependency Notes

• No additional Python dependencies.

• Assumes inkscape is available in the $PATH.

  • If unavailable, .wmf images are skipped with a warning.
  • This fallback behavior is safe and non-breaking.

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🧪 Tested With

• Linux (NixOS), Python 3.12

• Slide decks containing .png, .jpeg, .wmf, grouped shapes, and malformed objects

• Markdown output rendered via:

  pandoc out.md -t beamer -o out.pdf

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📎 Related

• Consolidates local improvements from university lecture slide conversion workflows.
• If accepted, enables better support for vector graphics and reduces conversion fragility.