Implement a more sophisticated markdown parsing engine (#145)

DiscordChatExporter.Core.Markdown/MentionNode.cs

@@ -0,0 +1,18 @@
+namespace DiscordChatExporter.Core.Markdown
+{
+    public class MentionNode : Node
+    {
+        public string Id { get; }
+
+        public MentionType Type { get; }
+
+        public MentionNode(string lexeme, string id, MentionType type)
+            : base(lexeme)
+        {
+            Id = id;
+            Type = type;
+        }
+
+        public override string ToString() => $"<{Type} mention> {Id}";
+    }
+}