add preprocessor for RST docs, see #2461 and #2431

The idea is to filter the sources, replacing @<var>@ occurrences with
the mapping for <var> (which is currently hard-coded). @@ -> @. In order
to make this work, I had to move the doc sources one directory down
(into akka-docs/rst) so that the filtered result could be in a sibling
directory so that relative links (to _sphinx plugins or real code) would
continue to work.

While I was at it I also changed it so that WARNINGs and ERRORs are not
swallowed into the debug dump anymore but printed at [warn] level
(minimum).

One piece of fallout is that the (online) html build is now run after
the normal one, not in parallel.

akka-docs/rst/scala/code/docs/routing/ConsistentHashingRouterDocSpec.scala

@@ -0,0 +1,73 @@
+/**
+ * Copyright (C) 2009-2012 Typesafe Inc. <http://www.typesafe.com>
+ */
+package docs.routing
+
+import akka.testkit.AkkaSpec
+import akka.testkit.ImplicitSender
+
+object ConsistentHashingRouterDocSpec {
+
+  //#cache-actor
+  import akka.actor.Actor
+  import akka.routing.ConsistentHashingRouter.ConsistentHashable
+
+  class Cache extends Actor {
+    var cache = Map.empty[String, String]
+
+    def receive = {
+      case Entry(key, value) ⇒ cache += (key -> value)
+      case Get(key)          ⇒ sender ! cache.get(key)
+      case Evict(key)        ⇒ cache -= key
+    }
+  }
+
+  case class Evict(key: String)
+
+  case class Get(key: String) extends ConsistentHashable {
+    override def consistentHashKey: Any = key
+  }
+
+  case class Entry(key: String, value: String)
+  //#cache-actor
+
+}
+
+class ConsistentHashingRouterDocSpec extends AkkaSpec with ImplicitSender {
+
+  import ConsistentHashingRouterDocSpec._
+
+  "demonstrate usage of ConsistentHashableRouter" in {
+
+    //#consistent-hashing-router
+    import akka.actor.Props
+    import akka.routing.ConsistentHashingRouter
+    import akka.routing.ConsistentHashingRouter.ConsistentHashMapping
+    import akka.routing.ConsistentHashingRouter.ConsistentHashableEnvelope
+
+    def hashMapping: ConsistentHashMapping = {
+      case Evict(key) ⇒ key
+    }
+
+    val cache = system.actorOf(Props[Cache].withRouter(ConsistentHashingRouter(10,
+      hashMapping = hashMapping)), name = "cache")
+
+    cache ! ConsistentHashableEnvelope(
+      message = Entry("hello", "HELLO"), hashKey = "hello")
+    cache ! ConsistentHashableEnvelope(
+      message = Entry("hi", "HI"), hashKey = "hi")
+
+    cache ! Get("hello")
+    expectMsg(Some("HELLO"))
+
+    cache ! Get("hi")
+    expectMsg(Some("HI"))
+
+    cache ! Evict("hi")
+    cache ! Get("hi")
+    expectMsg(None)
+
+    //#consistent-hashing-router
+  }
+
+}