Doctool: Remark plugins #61

This is a tracking issue for a new doctool using remark. The goals are:

• Render the api docs as HTML roughly equivalent to the existing doctool output.
• Render the guides and tutorials added to the nodejs/node repo as HTML.

This issue will contain all known breakages and necessary plugins (both existing and net new), broken into "required" and "nice to have":

Required

• @include syntax (remark-include by @Qard)
• Hook into Node Makefile
• YAML frontmatter (for stability index)
  • per-section YAML
• {Type} parsing (for parity with this PR)
• Basic layout selection (for switching between guides and API layouts)
• Header anchors

Nice to have

• Linting
  • ESLint for JS code examples
  • Link validation
  • API Method format validator
  • Make existing docs pass lint
  • Hook into Node Makefile tests
  • API headers — check to make sure they're in alphabetical order
• Switch table of contents generation to remark-toc