Add asn= and prefix= tags from a routewatch instance (closes #204)

SWW_ROUTEWATCH_URL names the instance. The new heuristic routewatch_tags
asks it in the background about each client and tags the request. Answers
are kept in memory for an hour. A request without tags gives the reason in
routewatch_tags_missing, and it is never delayed or refused.

Model: opus-5-5

internal/discriminator/discriminator.go

@@ -123,6 +123,7 @@ func New(params Params) *Server {
 		Lists:      h.lists,
 		DNSBL:      h.dnsbl,
 		AbuseIPDB:  h.abuseIPDB,
+		RouteWatch: h.routeWatch,
 		Metrics:    h.metrics,
 	}
 }