[Kinflou]

Restructures the Reference section.

Moves

• Package: reference/congregation/ (config.idp, comline.toml) moves to reference/package/congregation/, under a new Package section with the schema reference beside it.
• Schema reference keeps its URL at reference/schema/, and is listed under Package in the nav. The std pages' URL, reference/schema/std/, is linked from code: generation's STD_DOCS, which is the default std link in every comline doc output, and cli's docs and tests. Keeping the path avoids a cross-repo change.
• Conformance: reference/conformance.md splits into reference/conformance/ with these pages:
  • the pipeline;
  • wire conformance, which keeps the ops protocol, so #the-ops-protocol is now on conformance/wire;
  • generator conformance;
  • fuzzing;
  • benchmarks;
  • timings, size and coverage;
  • reports and the Observatory.
• CLI: reference/tools/cli.md becomes reference/tools/cli/index.md, beside inspect and doc. The URL is unchanged.
• Observatory: a new reference/tools/observatory.md, listed under Tools.

Follow-ups to the moves

• Links across the guides, the developer pages and the reference point at the new paths.
• The CLI-drift workflow and check-cli-drift.py point at cli/index.md.
• The nav.css cache-buster goes to v23.

Rebased onto main

These upstream changes are carried into the moved pages, with their links re-pointed:

• docs#160's specification_version row and comline fix row;
• docs#149/datagram@3 and comline@2 are the defaults #150's datagram@3 and comline@2 defaults;
• conformance --json;
• the generate row's wire-numbers text.

Every other upstream file is unchanged. Also fixes the Extending page's link to the Guides, which pointed one directory too shallow.

Checks

• zensical build --strict passes locally with no issues.
• The built site has reference/schema/std/http/ at its old URL, the moved pages, and the Editions section.