Add-on

I've cleaned up the code a bit by re-capitalizing the NPCEntityTargetEvent and removed the unused serial id number in it (looks like it was initially an exception class). I've also added in some more methods that have helped me in my plugin:

setSleeping(boolean flag);
* Sets whether the NPC looks like it is sleeping or not

isSleeping();
* Returns whether the NPC is in a sleeping state or not