Add Roles property to SocketGuildUser

there's a few different ways to select a user's roles from their role IDs, and this one seems to be the most efficient.

doesn't seem like there's any reason this shouldn't be included.

src/Discord.Net.WebSocket/Entities/Users/SocketGuildUser.cs

@@ -3,6 +3,7 @@ using System;
 using System.Collections.Generic;
 using System.Collections.Immutable;
 using System.Diagnostics;
+using System.Linq;
 using System.Threading.Tasks;
 using Model = Discord.API.GuildMember;
 using PresenceModel = Discord.API.Presence;
@@ -32,6 +33,7 @@ namespace Discord.WebSocket
         public bool IsDeafened => VoiceState?.IsDeafened ?? false;
         public bool IsMuted => VoiceState?.IsMuted ?? false;
         public DateTimeOffset? JoinedAt => DateTimeUtils.FromTicks(_joinedAtTicks);
+        public IEnumerable<SocketRole> Roles => _roleIds.Select(id => Guild.GetRole(id));
         public IReadOnlyCollection<ulong> RoleIds => _roleIds;
         public SocketVoiceChannel VoiceChannel => VoiceState?.VoiceChannel;
         public string VoiceSessionId => VoiceState?.VoiceSessionId ?? "";