tools: parse documentation metadata (take 2)

[addaleax]

Checklist

• tests and code linting passes
• a test and/or benchmark is included
• documentation is changed or added … kinda.
• the commit message follows commit guidelines

Affected core subsystem(s)

tools, doc

Description of change

This is a continuation of #3867. Original description:

---

This commit introduces the Documentation YAML metadata concept to the
documentation.

• Parses added or Added for HTML
• Parses all data for JSON

This is in prelude to #3713.

Markup would look like this:

## assert(value[, message]), assert.ok(value[, message])
<!-- YAML
added: v0.10.0
-->

---

Changed/additionally included in this PR:

• Rebased the original commit to master, and applied fixes so linting passes with the current rules.
• Allow the added: attribute to be a collection of versions rather than a single one, since semver-minors can trickle down to previous major versions.
• Add a deprecated: attribute.
• As an example, add these attributes in buffer.md to show how this will work in real life.

/cc @nodejs/documentation