Add prometheus metrics to the cache handler. This just used prometheus,
if the metrics middleware does not setup the handler, there is nobody
reading these metrics, but they are still reported. Seems the simplest
solution while keeping the whole middleware separation in tact.
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.
