Tool contract 11.18.0

The manual is reorganised into three groups, and every old address still answers.

• elixir_docs: an index page's group is now Use Elixir, Connect an AI or Build and reference. Eighteen new slugs hold what longer pages split into, among them connect-a-client, connecting, freshness-and-gaps, decks-and-war, timeline-tool, inactivity-clock and ladder-season.
• elixir_docs with a section that moved answers from its new page, under that page's slug. So does elixir://docs/<page>#<section>.
• Tool docs_ref pointers name the new homes.

Additive: no argument, field or error changed, and nothing changes for the JSON API.