Added UserStatus string enum

src/Discord.Net/Enums/UserStatus.cs

@@ -0,0 +1,12 @@
+namespace Discord
+{
+    public static class UserStatus
+	{
+		/// <summary> User is currently online and active. </summary>
+		public const string Online = "online";
+		/// <summary> User is currently online but inactive. </summary>
+		public const string Away = "away";
+		/// <summary> User is offline. </summary>
+		public const string Offline = "offline";
+	}
+}