memory.c: Remove a lone #ifndef GAMEPAK_FITS_IN_RAM.
cpu_c.c: Delete. It goes counter to the purpose of the emulator.
Switch to on-demand loading and memory-mapped files where available.

GCW Zero: Report decompression progress and which files are being loaded/saved during startup and shutdown.
GCW Zero: Load entire ROMs into memory again. Dingoo A320: Keep memory-mapping files due to the device not having enough memory to hold 32 MiB ROMs in private allocations.
OpenDingux: Implement button remapping saved to file.

More technically:
* Custom persistence functions for mappings to save them to a file in a format that makes sense (^ v < > L R A B X Y S s, with X and Y under the SNES/Nintendo DS/Dingoo A320 mapping, S for Start and s for Select).
* Merge the GCW Zero and Dingoo A320 input code, dealing with the face button placement issue (X and Y are reversed on one compared to the other) by having different descriptions #ifdef GCW_ZERO and #ifdef DINGOO_A320.
* Custom functions to nullify Left/Right, to display button remapping values and to get buttons for mapping.
* Display settings are now in their own submenu.
* There is now a way to get raw button presses in the GUI.
OpenDingux: Ignore progress for battery saving, because it flashes in-game.
OpenDingux: Attempt to optimise the display of borders by stopping to draw them when it's certain that all of the back buffers of the surface have no remaining image from the menu (green) or progress screen (black).
OpenDingux: Implement a fast-forward hotkey and save it to the configuration file. Also fix up button mappings if nothing is bound to a GBA key or the Menu action.
OpenDingux: Fix self-overlapping FPS counter caused by commit 9d0e7a5405882c9ce982b5b0e79cb2f45612ad8f.
OpenDingux: Improve fast-forwarding. Better detection of the need to increase frame skipping when there is insufficient buffered audio, and to raise the frame rate again once a fair amount of time has passed without audio underruns. This may help the Dingoo A320.
OpenDingux: Allow the analog directions to be mapped to hotkeys and buttons.
OpenDingux: Require ONLY the Y key to be pressed in order to enter the menu.
Clean Makefiles a little bit