server/config: Generic caching backend.

luci_config/server/cfgclient/backend/caching/doc.go

+// Copyright 2015 The LUCI Authors. All rights reserved.
+// Use of this source code is governed under the Apache License, Version 2.0
+// that can be found in the LICENSE file.
+
+// Package caching implements a config.Interface that uses a caching layer to
+// store its configuration values.
+//
+// The Backend in this package is generic, and does not implement that actual
+// caching interface. Instead, the user should pair it with a cache
+// implementation by implementing its CacheGet method.
+//
+// Some example caches include:
+//      - Process in-memory cache (proccache).
+//      - memcache, or AppEngine's memcache service.
+//      - A local storage cache (e.g., on-disk)
+//      - A datastore cache.
+package caching