don't render rmd as markdown

[kivikakk]

Reverts #343 by user request -- R Markdown includes a lot of information that a regular Markdown renderer will omit, in such a way that there's no indication anything is missing.

/cc @yihui @karthik @jennybc

[kivikakk]

I'll merge this PR once CI goes green -- getting the latest version of github/markup running on github.com itself will take a little more time, as we're currently in code freeze for GitHub Universe. Once we're through, I'll update the live version and update you all here to know it's done!

[yihui]

Hi @kivikakk, I wonder if it is possible to enable soft-wrapping for Rmd files. It only requires a simple CSS change in Github's UI:

.type-rmarkdown .blob-code-inner {
  white-space: pre-wrap;
}

BTW, for the record, I have written down the rationale for this PR and #1237 in this blog post: https://yihui.name/en/2018/10/rmd-github/

[kivikakk]

@yihui I've opened an issue internally to see about this change. I'll let you know!

[corinalogan]

@kivikakk I would LOVE it if @yihui's solution could be implemented asap. I am a researcher and my .Rmd files are currently under peer review. Soft wrapping the text will make it possible for my papers to continue through the peer review process because reviewers aren't usually .Rmd savvy and they will probably not bother to scroll horizontally.