Format file references as markdown links

When referencing files in your output, always format them as markdown links. Use the GitHub-style #L fragment for line numbers.

Format

With a line number:

[filename.el:42](relative/path/to/filename.el#L42)

With a line range:

[filename.el:42-50](relative/path/to/filename.el#L42-L50)

Without a line number: