Move Mupen64Plus into its own repository and add it as submodule.
Move NeoPop core into its own repository and add it as a submodule.
Move Nestopia core into its own repository and add it as a submodule.
Move SNES9x core into its own repository and add it as a submodule.
Move VisualBoyAdvance into its own repository and add it as a submodule.