Frontmatter rendering in Markdown for TOML and JSON

Problem to solve

GitLab Markdown display should render frontmatter in other formats besides just YAML.

Further details

The popular static site generator Hugo supports YAML, TOML, and JSON.

Proposal

At minimum, support at least YAML, TOML, and JSON. Arbitrary specification could be a nice bonus.

What does success look like, and how can we measure that?

Frontmatter in Markdown files in various formats render as expected.

Links / references

Demonstration project on GitLab.com with example files: https://gitlab.com/travismiller/gitlab-frontmatter