This allows more flexibility when loading games in libretro builds,
since we can now load games either from a directory or from a ZIP or 7Z
archive. Also, the path cache is now active for all filesystem calls
made from inside Ruby.
I've made it so that `Graphics.update` pauses the Ruby VM and returns to
the libretro frontend. Once the libretro frontend calls `retro_run()`
again, the Ruby VM resumes. This allows the libretro frontend to control
the rendering loop.
