Add a way to have ruleset-specific configs

osu.Game/Rulesets/Configuration/RulesetConfigManager.cs

@@ -0,0 +1,24 @@
+// Copyright (c) 2007-2018 ppy Pty Ltd <contact@ppy.sh>.
+// Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
+
+using osu.Framework.Configuration;
+using osu.Framework.Platform;
+
+namespace osu.Game.Rulesets.Configuration
+{
+    public abstract class RulesetConfigManager<T> : ConfigManager<T>, IRulesetConfigManager
+        where T : struct
+    {
+        protected override string Filename => ruleset?.ShortName;
+        private readonly Ruleset ruleset;
+
+        protected RulesetConfigManager(Ruleset ruleset, Storage storage)
+            : base(storage)
+        {
+            this.ruleset = ruleset;
+
+            // Re-load with the ruleset
+            Load();
+        }
+    }
+}