We should move all the assorted mob/animal statistics out to a separate NpeData class, which can include...

• Number of kills by players
• Number of kills by environment
• Number of kills by other non-player entities (this might not actually happen, but we can find out)
• Number of players killed
• Number of other non-player entities killed (if it turns out that this actually happens)

This NpeData class will be instantiated in a hash table, similar to PlayerData and BlockData, and indexed by the entity's class name. This advent will also provide us with a good model to not have to hardcode each new animal/mob type, which will solve #19 for us for free.

Fixed in 94c7b5b

Since this branch hasn't been merged in yet, reopening this to rename the NpeData death stats to something more clear