RTC for FatFs filetimes. Saves subdir support.

[ds-sloth]

• Added RTC call (copied from GBARunner2's implementation) to ARM9 FatFs module. Update modification time of game save whenever game is launched. (Commits 7908e7d and 4a4543f)
• Added option to emulator settings menu to store game saves in a "./saves/" subdirectory of the ROM file's directory. Exactly like TWiLightMenu++. Off by default (of course). (Commits 0b23ba8 and e14d6e0)

Tested on DSi (DS-mode flashcard and TWiLightMenu++) and 3DS (TWiLightMenu++).

Please let me know if any of the code I've submitted is not clear or if you find any bugs when testing it.

Thanks for your consideration!

[Corshi]

Sorry, but could you share your build .nds files, on your site https://github.com/ds-sloth/GBARunner2.git

I try to create them myself, but I run into Makefile error code 2. I'm on Win7, using msys2, instead of win10's linux add-on.