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/SPI.cpp

@@ -463,6 +463,7 @@ void SetupDirectBoot(bool dsi)
     }
 }
 
+u32 GetFirmwareLength() { return FirmwareLength; }
 u8 GetConsoleType() { return Firmware[0x1D]; }
 u8 GetWifiVersion() { return Firmware[0x2F]; }
 u8 GetNWifiVersion() { return Firmware[0x1FD]; } // for DSi; will return 0xFF on a DS