Parse emojis in markdown and render them using Twemoji

Closes #140

DiscordChatExporter.Core/Models/Emoji.cs

@@ -1,10 +1,12 @@
-using Tyrrrz.Extensions;
+using System.Collections.Generic;
+using System.Linq;
+using Tyrrrz.Extensions;
 
 namespace DiscordChatExporter.Core.Models
 {
     // https://discordapp.com/developers/docs/resources/emoji#emoji-object
 
-    public class Emoji
+    public partial class Emoji
     {
         public string Id { get; }
 
@@ -28,8 +30,7 @@ namespace DiscordChatExporter.Core.Models
                 }
 
                 // Standard unicode emoji (via twemoji)
-                var codePoint = char.ConvertToUtf32(Name, 0).ToString("x");
-                return $"https://twemoji.maxcdn.com/2/72x72/{codePoint}.png";
+                return $"https://twemoji.maxcdn.com/2/72x72/{GetTwemojiName(Name)}.png";
             }
         }
 
@@ -40,4 +41,16 @@ namespace DiscordChatExporter.Core.Models
             IsAnimated = isAnimated;
         }
     }
+
+    public partial class Emoji
+    {
+        private static IEnumerable<int> GetCodePoints(string emoji)
+        {
+            for (var i = 0; i < emoji.Length; i += char.IsHighSurrogate(emoji[i]) ? 2 : 1)
+                yield return char.ConvertToUtf32(emoji, i);
+        }
+
+        private static string GetTwemojiName(string emoji)
+            => GetCodePoints(emoji).Select(i => i.ToString("x")).JoinToString("-");
+    }
 }