Added Prefix check extensions to IMessage

src/Discord.Net.Commands/Extensions/MessageExtensions.cs

@@ -0,0 +1,44 @@
+namespace Discord.Commands
+{
+    public static class MessageExtensions
+    {
+        public static bool HasCharPrefix(this IMessage msg, char c, ref int argPos)
+        {
+            var text = msg.RawText;
+            if (text.Length > 0 && text[0] == c)
+            {
+                argPos = 1;
+                return true;
+            }
+            return false;
+        }
+        public static bool HasStringPrefix(this IMessage msg, string str, ref int argPos)
+        {
+            var text = msg.RawText;
+            str = str + ' ';
+            if (text.StartsWith(str))
+            {
+                argPos = str.Length;
+                return true;
+            }
+            return false;
+        }
+        public static bool HasMentionPrefix(this IMessage msg, IUser user, ref int argPos)
+        {
+            var text = msg.RawText;
+            string mention = user.Mention + ' ';
+            if (text.StartsWith(mention))
+            {
+                argPos = mention.Length;
+                return true;
+            }
+            string nickMention = user.NicknameMention + ' ';
+            if (text.StartsWith(mention))
+            {
+                argPos = nickMention.Length;
+                return true;
+            }
+            return false;
+        }
+    }
+}