Say which bytes the byte limits count, and what passing one does (closes #203)

Documents only. The byte limits and byte anomaly thresholds count body
bytes, as SWW_BYTES_COUNT chooses them, with WebSocket traffic each way,
once a response has ended; the request that passes a limit is not cut
off and the client is banned. README.md, SPEC.md and docs/ now say so,
and no longer call a response's bytes the request's. Also made plain:
rate limits and their exemptions, the refusal threshold,
SWRP_MAX_REQUEST_TIME_MS, SWRP_MAX_RESPONSE_SIZE, SWW_LOOKUP_SOURCE,
SWW_LIMIT_BAN_REPEAT_WINDOW, the metrics' byte series, and the SPEC.md
claim about answering within SWRP_TIMEOUT_MS. EVALUATION.md is audited
too; its survey facts and date are unchanged.

Model: fable-5-1 (first audit); opus-5-5 (rework)

docs/state-files.md

@@ -61,7 +61,7 @@ since it was first seen:
 - the first and last time seen;
 - the AS number, AS name and country last looked up, and when;
 - total requests, and how many were forwarded and how many refused;
-- bytes in each direction;
+- body bytes of its requests, and of the responses it was sent;
 - responses by status class;
 - offences by kind: `limit`, `attack`, `rule_blocked` and `waf_blocked`. A file
   may also hold `token_refused`, which is kept, and which nothing adds to.