pandoc error in processing about markdown-mode-guide

[jrblevin]

This was an early Make rule I used for quick local Previews using Pandoc. Unfortunately, it no longer works since Pandoc doesn't recognize much of the Leanpub-specific syntax that is now used, so I'll remove it. At this point, the full Leanpub toolchain is needed to produce a PDF.

The root issue is that some of the fenced code blocks with attributes aren't being processed as code blocks, and so some \n strings are making it through to LaTeX, which is trying to interpret them as macros, but they aren't.