Cleanup docs and the chaos middleware

Make the CH middleware actually work. Needs a bit of a hack to route

the fake version.bind and friends zone to the correct handler. Fiddle

with the order in directive.go so that CH queries get logged as well.



Secondly add class rewriting to the rewrite middleware handler and also

log the class by default.

middleware/middleware.go

@@ -20,6 +20,7 @@ type (
 	// If ServeDNS writes to the response body, it should return a status
 	// code of 0. This signals to other handlers above it that the response
 	// body is already written, and that they should not write to it also.
+	// TODO(miek): explain return codes better.
 	//
 	// If ServeDNS encounters an error, it should return the error value
 	// so it can be logged by designated error-handling middleware.