replace unicode arrows

* ⇒, →, ←
* because we don't want to show them in documentation snippets and
  then it's complicated to avoid that when snippets are
  located in src/test/scala in individual modules
* dont replace object `→` in FSM.scala and PersistentFSM.scala

akka-docs/src/test/scala/docs/remoting/RemoteDeploymentDocSpec.scala

@@ -14,7 +14,7 @@ import akka.remote.RemoteScope
 object RemoteDeploymentDocSpec {
 
   class SampleActor extends Actor {
-    def receive = { case _ ⇒ sender() ! self }
+    def receive = { case _ => sender() ! self }
   }
 
 }