Added CommandContext, fixed commands compile errors

src/Discord.Net.Commands/CommandContext.cs

@@ -0,0 +1,18 @@
+namespace Discord.Commands
+{
+    public struct CommandContext
+    {
+        public IGuild Guild { get; }
+        public IMessageChannel Channel { get; }
+        public IUser User { get; }
+        public IUserMessage Message { get; }
+
+        internal CommandContext(IGuild guild, IMessageChannel channel, IUser user, IUserMessage msg)
+        {
+            Guild = guild;
+            Channel = channel;
+            User = user;
+            Message = msg;
+        }
+    }
+}