Custom path support (#1333)

also including:
* getting rid of shitty strings
* all new, cleaner ROM handling code
* base for DSi savestates
* GBA slot addons (for now, memory cart)

src/frontend/qt_sdl/SaveManager.h

@@ -0,0 +1,70 @@
+/*
+    Copyright 2016-2021 Arisotura
+
+    This file is part of melonDS.
+
+    melonDS is free software: you can redistribute it and/or modify it under
+    the terms of the GNU General Public License as published by the Free
+    Software Foundation, either version 3 of the License, or (at your option)
+    any later version.
+
+    melonDS is distributed in the hope that it will be useful, but WITHOUT ANY
+    WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+    FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License along
+    with melonDS. If not, see http://www.gnu.org/licenses/.
+*/
+
+#ifndef SAVEMANAGER_H
+#define SAVEMANAGER_H
+
+#include <string>
+#include <unistd.h>
+#include <time.h>
+#include <atomic>
+#include <QThread>
+#include <QMutex>
+
+#include "types.h"
+
+class SaveManager : public QThread
+{
+    Q_OBJECT
+    void run() override;
+
+public:
+    SaveManager(std::string path);
+    ~SaveManager();
+
+    std::string GetPath();
+    void SetPath(std::string path, bool reload);
+
+    void RequestFlush(const u8* savedata, u32 savelen, u32 writeoffset, u32 writelen);
+    void CheckFlush();
+
+    bool NeedsFlush();
+    void FlushSecondaryBuffer(u8* dst = nullptr, u32 dstLength = 0);
+
+private:
+    std::string Path;
+
+    std::atomic_bool Running;
+
+    u8* Buffer;
+    u32 Length;
+    bool FlushRequested;
+
+    QMutex* SecondaryBufferLock;
+    u8* SecondaryBuffer;
+    u32 SecondaryBufferLength;
+
+    time_t TimeAtLastFlushRequest;
+
+    // We keep versions in case the user closes the application before
+    // a flush cycle is finished.
+    u32 PreviousFlushVersion;
+    u32 FlushVersion;
+};
+
+#endif // SAVEMANAGER_H