Wikilink support

Support links in the format,

[[Other document]]

Where "Other document" maps to an "Other document.md" file.

Look at the code that parses markdown links in the project, likely in a parser or transformer file. Understand how file paths are resolved relative to the source document. Implement recognition of [[...]] syntax and map it to the corresponding .md file. Test by running the tool on a sample with wikilinks.

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