This is an ugly hack that allows both exporting additional functions
(incl. methods via static function + void* userArg) to Game DLLs
and setting callback functions from the Game DLL that the Engine will
call, without breaking the Game API (again after this change).
This is mostly meant for replacing ugly hacks with SourceHook and
similar and mods (yes, this is still an ugly hack, but less ugly).
See the huge comment in Common.h for more information.
Right now the only thing implemented is a Callback for when images
are reloaded (via reloadImages or vid_restart) - Ruiner needs that.
Also increased GAME_API_VERSION to 9, because this breaks the A[PB]I
(hopefully after the next release it won't be broken in the foreseeable
future)
