Add ruleset and skin resource stub.

Assets/Cryville/Crtr/Ruleset.cs

@@ -1,5 +1,6 @@
 using Cryville.Common;
 using Cryville.Common.Pdt;
+using Cryville.Crtr.Browsing;
 using Newtonsoft.Json;
 using System;
 using System.Collections.Generic;
@@ -10,7 +11,7 @@ using System.Text.RegularExpressions;
 using SIdentifier = Cryville.Common.Identifier;
 
 namespace Cryville.Crtr {
-	public class Ruleset {
+	public class Ruleset : MetaInfo {
 		[JsonRequired]
 		public long format;