Pandoc is crashing on Windows

[znmeb]

I've run into some Pandoc problems knitting the vignette on Windows. See https://github.com/jgm/pandoc/issues/5037

Everything seems to be working on Linux, so I made a test branch for the RStudio / Pandoc teams called pandoc-testing. I'll keep working on the rest of the package without the vignette unless the Pandoc fix shows up in the next day or two.