move code to src/test

* so that it compiles and tests pass
* fix some additional snip references in getting started

akka-docs/src/test/scala/docs/ddata/TwoPhaseSet.scala

@@ -0,0 +1,29 @@
+/**
+ * Copyright (C) 2015-2017 Lightbend Inc. <http://www.lightbend.com>
+ */
+package docs.ddata
+
+import akka.cluster.ddata.ReplicatedData
+import akka.cluster.ddata.GSet
+
+//#twophaseset
+case class TwoPhaseSet(
+  adds:     GSet[String] = GSet.empty,
+  removals: GSet[String] = GSet.empty)
+  extends ReplicatedData {
+  type T = TwoPhaseSet
+
+  def add(element: String): TwoPhaseSet =
+    copy(adds = adds.add(element))
+
+  def remove(element: String): TwoPhaseSet =
+    copy(removals = removals.add(element))
+
+  def elements: Set[String] = adds.elements diff removals.elements
+
+  override def merge(that: TwoPhaseSet): TwoPhaseSet =
+    copy(
+      adds = this.adds.merge(that.adds),
+      removals = this.removals.merge(that.removals))
+}
+//#twophaseset