How we migrated to CommonMark

What this post added

This post details GitLab's migration from RedCarpet to CommonMark for Markdown rendering. It outlines the motivation for the migration, focusing on the inconsistencies of various Markdown flavors and the goal of achieving consistent rendering across platforms. The migration was executed in three phases: initially only for new content, then extending to repository and wiki files, and finally removing RedCarpet entirely. The post also highlights improvements made upstream to the cmark-gfm library, specifically regarding strikethrough syntax and a bug fix for table rendering. A tool, diff_redcarpet_cmark, was developed to assist in converting existing content.