[Enhancement] Bigger SD card size support

[joeyjpg]

Hello!

I decided, wouldn't it be fun if i had my DSi, but on my computer?
So, i dump the stuff from my DSi, plug the SD card into my computer, give the emulator the files needed, yada yada, set the SD card size to 4 GB and point it to /dev/sdc for the image, boot the firmware, works fine.

Until..
I go into my (totally legal) roms folder, to the SNES folder, only to find it empty. The NES folder? Corrupt. Five NDS roms? Corrupt.

So i go check how much of the SD card is in use, only to find i'm 1.1 GB over what MelonDS wants to read.
Then i go into the settings, thinking "maybe it can go higher?" NEIN! It can not.
I go into the settings file, thinking "maybe they just put the size there in bytes" but NAHH, they have the option number there. Can't blame them though, knowing that that's alot simpler.

So, all i'd like to suggest here, is one of two things:

Up the very limit of the SD image size to 32 (or 16, idk) GB,
Or let the user enter an image size manually.

Thanks in advance!