Add support for Guild Member object & included data (#279)

DiscordChatExporter.Core.Models/Member.cs

@@ -0,0 +1,20 @@
+using System.Collections.Generic;
+using System.Linq;
+
+namespace DiscordChatExporter.Core.Models
+{
+    public class Member
+    {
+        public string UserId { get; }
+        public string? Nick { get; }
+
+        public IReadOnlyList<string> Roles { get; }
+
+        public Member(string userId, string? nick, IReadOnlyList<string> roles)
+        {
+            UserId = userId;
+            Nick = nick;
+            Roles = roles;
+        }
+    }
+}