Add support for AudioPlay.Play directive

Alexa.NET/Response/Directive/AudioItem.cs

@@ -0,0 +1,11 @@
+using Newtonsoft.Json;
+
+namespace Alexa.NET.Response.Directive
+{
+    public class AudioItem
+    {
+        [JsonRequired]
+        [JsonProperty("stream")]
+        public AudioItemStream Stream { get; set; }
+    }
+}

Alexa.NET/Response/Directive/AudioItemStream.cs

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+using Newtonsoft.Json;
+
+namespace Alexa.NET.Response.Directive
+{
+    public class AudioItemStream
+    {
+        [JsonRequired]
+        [JsonProperty("url")]
+        public string Url { get; set; }
+
+        [JsonRequired]
+        [JsonProperty("token")]
+        public string Token { get; set; }
+
+        [JsonRequired]
+        [JsonProperty("expectedPreviousToken")]
+        public string ExpectedPreviousToken { get; set; }
+
+        [JsonRequired]
+        [JsonProperty("offsetInMilliseconds")]
+        public int OffsetInMilliseconds { get; set; }
+    }
+}

Alexa.NET/Response/Directive/AudioPlayerPlayDirective.cs

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+using Newtonsoft.Json;
+using Newtonsoft.Json.Converters;
+
+namespace Alexa.NET.Response.Directive
+{
+    public class AudioPlayerDirective : IDirective
+    {
+        [JsonProperty("playBehavior")]
+        [JsonRequired]
+        [JsonConverter(typeof(StringEnumConverter))]
+        public PlayBehavior PlayBehavior { get; set; }
+
+        [JsonProperty("audioItem")]
+        [JsonRequired]
+        public AudioItem AudioPlayerAudioItem { get; set; }
+
+        [JsonProperty("type")]
+        public string Type => "AudioPlayer.Play";
+    }
+}

Alexa.NET/Response/Directive/PlayBehavior.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Runtime.Serialization;
+using System.Threading.Tasks;
+
+namespace Alexa.NET.Response.Directive
+{
+    public enum PlayBehavior
+    {
+        [EnumMember(Value = "REPLACE_ALL")]
+        ReplaceAll,
+        [EnumMember(Value = "ENQUEUE")]
+        Enqueue,
+        [EnumMember(Value = "REPLACE_ENQUEUED")]
+        ReplaceEnqueued
+    }
+}