SPEC: the one place for behaviour and reasons; docs/ as lookup lists only

docs/core-rule-set.md, docs/lookup.md, docs/reputation.md and docs/bans.md
restated the spec and are folded back into it and removed. The remaining
docs files hold only lists: settings with their defaults and value forms,
the request log's fields, the metrics, the endpoints, the state files and
their contents, the rule file format and default file, the alert events
and messages, the image's contents and pins, and the gitea notes. Every
behaviour each of them held moves to the spec, said once. The settings
groups have the same names in both files. Stale comments in
internal/state and script/example-app point at the right places.

Model: fable-5-1

internal/state/state.go

@@ -1,5 +1,6 @@
 // Package state keeps smallwebwaf's state in JSON files in
-// SWWAF_STATE_DIR, as the "Persistent state" section of SPEC.md describes:
+// SWWAF_STATE_DIR, as the "Persistent state" section of SPEC.md requires
+// and docs/state-files.md lists them:
 // bans.json holds the bans, clients.json each client's counters and
 // history, lookups.json GeoJS's answers, reputation.json the last try and
 // last good copy of each list fetched from a URL, the DNSBL zones'