Refactor InnerFAT into Savegame and Extdata

And derive TitleDB from it too.

src/core/savegame.h

@@ -0,0 +1,30 @@
+// Copyright 2021 threeSD Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include "core/inner_fat.hpp"
+
+namespace Core {
+
+class Savegame final : public Archive<Savegame> {
+public:
+    explicit Savegame(std::vector<std::vector<u8>> partitions);
+    ~Savegame();
+
+    bool IsGood() const;
+    bool Extract(std::string path) const;
+
+private:
+    bool CheckMagic() const;
+    bool ExtractFile(const std::string& path, std::size_t index) const;
+    ArchiveFormatInfo GetFormatInfo() const;
+
+    bool is_good = false;
+
+    friend class Archive<Savegame>;
+    friend class InnerFAT<Savegame>;
+};
+
+} // namespace Core