Added RPC channel and guild entities, Get and Select methods

src/Discord.Net.Rpc/API/Rpc/Message.cs

@@ -0,0 +1,17 @@
+using Newtonsoft.Json;
+
+namespace Discord.API.Rpc
+{
+    public class Message : Discord.API.Message
+    {
+        [JsonProperty("blocked")]
+        public Optional<bool> IsBlocked { get; }
+        [JsonProperty("content_parsed")]
+        public Optional<object[]> ContentParsed { get; }
+        [JsonProperty("author_color")]
+        public Optional<string> AuthorColor { get; } //#Hex
+
+        [JsonProperty("mentions")]
+        public new Optional<ulong[]> UserMentions { get; set; }
+    }
+}