Repurpose reason field

src/Discord.Net.Rest/DiscordRestApiClient.cs

@@ -1645,8 +1645,9 @@ namespace Discord.API
             options = RequestOptions.CreateOrClone(options);
 
             var ids = new BucketIds(guildId: guildId);
-            string reason = string.IsNullOrWhiteSpace(args.Reason) ? "" : $"&reason={Uri.EscapeDataString(args.Reason)}";
-            await SendAsync("PUT", () => $"guilds/{guildId}/bans/{userId}?delete_message_days={args.DeleteMessageDays}{reason}", ids, options: options).ConfigureAwait(false);
+            if (!string.IsNullOrWhiteSpace(args.Reason))
+                options.AuditLogReason = args.Reason;
+            await SendAsync("PUT", () => $"guilds/{guildId}/bans/{userId}?delete_message_days={args.DeleteMessageDays}", ids, options: options).ConfigureAwait(false);
         }
         /// <exception cref="ArgumentException"><paramref name="guildId"/> and <paramref name="userId"/> must not be equal to zero.</exception>
         public async Task RemoveGuildBanAsync(ulong guildId, ulong userId, RequestOptions options = null)
@@ -1851,8 +1852,9 @@ namespace Discord.API
             options = RequestOptions.CreateOrClone(options);
 
             var ids = new BucketIds(guildId: guildId);
-            reason = string.IsNullOrWhiteSpace(reason) ? "" : $"?reason={Uri.EscapeDataString(reason)}";
-            await SendAsync("DELETE", () => $"guilds/{guildId}/members/{userId}{reason}", ids, options: options).ConfigureAwait(false);
+            if (!string.IsNullOrWhiteSpace(reason))
+                options.AuditLogReason = reason;
+            await SendAsync("DELETE", () => $"guilds/{guildId}/members/{userId}", ids, options: options).ConfigureAwait(false);
         }
         public async Task ModifyGuildMemberAsync(ulong guildId, ulong userId, Rest.ModifyGuildMemberParams args, RequestOptions options = null)
         {