=doc #3685 Add FAQ to documentation

* The links at http://akka.io will changed to point at this faq
* Some rewording of guarantees/reliability

akka-docs/rst/additional/code/docs/faq/Faq.scala

@@ -0,0 +1,27 @@
+package docs.faq
+
+import akka.actor.Actor
+
+//#exhaustiveness-check
+object MyActor {
+  // these are the messages we accept
+  sealed abstract trait Message
+  case class FooMessage(foo: String) extends Message
+  case class BarMessage(bar: Int) extends Message
+
+  // these are the replies we send
+  sealed abstract trait Reply
+  case class BazMessage(baz: String) extends Reply
+}
+
+class MyActor extends Actor {
+  import MyActor._
+  def receive = {
+    case message: Message ⇒ message match {
+      case BarMessage(bar) => sender ! BazMessage("Got " + bar)
+      // warning here: 
+      // "match may not be exhaustive. It would fail on the following input: FooMessage(_)"
+    }
+  }
+}
+//#exhaustiveness-check

akka-docs/rst/additional/code/docs/osgi/Activator.scala

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+package docs.osgi
+
+case object SomeMessage
+
+class SomeActor extends akka.actor.Actor {
+  def receive = { case SomeMessage => }
+}
+
+//#Activator
+import akka.actor.{ Props, ActorSystem }
+import org.osgi.framework.BundleContext
+import akka.osgi.ActorSystemActivator
+
+class Activator extends ActorSystemActivator {
+
+  def configure(context: BundleContext, system: ActorSystem) {
+    // optionally register the ActorSystem in the OSGi Service Registry
+    registerService(context, system)
+
+    val someActor = system.actorOf(Props[SomeActor], name = "someName")
+    someActor ! SomeMessage
+  }
+
+}
+//#Activator

akka-docs/rst/additional/code/docs/osgi/blueprint.xml

@@ -0,0 +1,14 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<blueprint xmlns="http://www.osgi.org/xmlns/blueprint/v1.0.0"
+           xmlns:akka="http://akka.io/xmlns/blueprint/v1.0.0">
+
+    <akka:actor-system name="BlueprintSystem" />
+
+    <akka:actor-system name="BlueprintSystemWithConfig">
+        <akka:config>
+            some.config {
+              key=value
+            }
+        </akka:config>
+    </akka:actor-system>
+</blueprint>