Feature: CustomStatusGame Activity (#1406)

* Implement CustomStatusGame activity

Adds the CustomStatusGame class, which is the activity corresponding to the custom status feature.

* Remove unused import from Game.cs

src/Discord.Net.Core/Entities/Activities/ActivityType.cs

@@ -20,6 +20,10 @@ namespace Discord
         /// <summary>
         ///     The user is watching some form of media.
         /// </summary>
-        Watching = 3
+        Watching = 3,
+        /// <summary>
+        ///     The user has set a custom status.
+        /// </summary>
+        CustomStatus = 4,
     }
 }

src/Discord.Net.Core/Entities/Activities/CustomStatusGame.cs

@@ -0,0 +1,40 @@
+using System;
+using System.Diagnostics;
+
+namespace Discord
+{
+    /// <summary>
+    ///     A user's activity for their custom status.
+    /// </summary>
+    [DebuggerDisplay(@"{DebuggerDisplay,nq}")]
+    public class CustomStatusGame : Game
+    {
+        internal CustomStatusGame() { }
+
+        /// <summary>
+        ///     Gets the emote, if it is set.
+        /// </summary>
+        /// <returns>
+        ///     An <see cref="IEmote"/> containing the <see cref="Emoji"/> or <see cref="GuildEmote"/> set by the user.
+        /// </returns>
+        public IEmote Emote { get; internal set; }
+
+        /// <summary>
+        ///     Gets the timestamp of when this status was created.
+        /// </summary>
+        /// <returns>
+        ///     A <see cref="DateTimeOffset"/> containing the time when this status was created.
+        /// </returns>
+        public DateTimeOffset CreatedAt { get; internal set; }
+
+        /// <summary>
+        ///     Gets the state of the status.
+        /// </summary>
+        public string State { get; internal set; }
+
+        public override string ToString()
+            => $"{Emote} {State}";
+
+        private string DebuggerDisplay => $"{Name}";
+    }
+}