Start lightweight client

This is the beginning of a lightweight client, which talks to the
server over Contraband-generated JSON API. Given that the server is
started on port 5173:

```
$ cd /tmp/bogus
$ sbt client localhost:5173
> compile
StatusEvent(Processing, Vector(compile, server))
StatusEvent(Ready, Vector())
StatusEvent(Processing, Vector(, server))
StatusEvent(Ready, Vector())
```

protocol/src/main/scala/sbt/protocol/Serialization.scala

@@ -0,0 +1,63 @@
+/*
+ * Copyright (C) 2016 Lightbend Inc. <http://www.typesafe.com>
+ */
+package sbt
+package protocol
+
+import sjsonnew.support.scalajson.unsafe.{ Converter, CompactPrinter }
+import scala.json.ast.unsafe.JValue
+import sjsonnew.support.scalajson.unsafe.Parser
+import java.nio.ByteBuffer
+import scala.util.{ Success, Failure }
+
+object Serialization {
+  def serializeCommand(command: CommandMessage): Array[Byte] =
+    {
+      import codec.JsonProtocol._
+      val json: JValue = Converter.toJson[CommandMessage](command).get
+      CompactPrinter(json).getBytes("UTF-8")
+    }
+
+  def serializeEvent(event: EventMessage): Array[Byte] =
+    {
+      import codec.JsonProtocol._
+      val json: JValue = Converter.toJson[EventMessage](event).get
+      CompactPrinter(json).getBytes("UTF-8")
+    }
+
+  /**
+   * @return A command or an invalid input description
+   */
+  def deserializeCommand(bytes: Seq[Byte]): Either[String, CommandMessage] =
+    {
+      val buffer = ByteBuffer.wrap(bytes.toArray)
+      Parser.parseFromByteBuffer(buffer) match {
+        case Success(json) =>
+          import codec.JsonProtocol._
+          Converter.fromJson[CommandMessage](json) match {
+            case Success(command) => Right(command)
+            case Failure(e)       => Left(e.getMessage)
+          }
+        case Failure(e) =>
+          Left(s"Parse error: ${e.getMessage}")
+      }
+    }
+
+  /**
+   * @return A command or an invalid input description
+   */
+  def deserializeEvent(bytes: Seq[Byte]): Either[String, EventMessage] =
+    {
+      val buffer = ByteBuffer.wrap(bytes.toArray)
+      Parser.parseFromByteBuffer(buffer) match {
+        case Success(json) =>
+          import codec.JsonProtocol._
+          Converter.fromJson[EventMessage](json) match {
+            case Success(event) => Right(event)
+            case Failure(e)     => Left(e.getMessage)
+          }
+        case Failure(e) =>
+          Left(s"Parse error: ${e.getMessage}")
+      }
+    }
+}