Adjustable spawning rates for monsters

I would love to have more possibilities to adjust the difficulty of the game. A slider to change the spawn rates of monsters (individually or overall) would be VERY helpful, much more helpful than the difficulty-setting since that affects hunger as well as monsters.

I myself would adjust it down but others may want to increase the amount of aggressive mobs. Both parties would benefit A LOT from this minor change which probably only amounts to adding a menu and making some previously hard-coded variable accessible to the player/serverhoster.