middleware/proxy: make it scale (#287)

* middleware/proxy

Use connection pooling for communicating with an upstream, instead of
opening a new socket every time.

This makes the proxy more efficient and allowed for some cleanups.

* Some cleanups

* Some fixes

* more

* Kill pool

* Add nil check

* remove pool

middleware/cache/cache.go

@@ -1,3 +1,4 @@
+// Package cache implements a cache.
 package cache
 
 import (