Implemented basic damage methods

After a bit of testing, it appears to work fine. With players it does properly update them, and give them the respawn screen when they die.

https://github.com/GlowstoneMC/Glowkit/pull/33 is required
I know I said otherwise in IRC, but instead of making an empty method for this, just leave a `// todo` where it would be called. Also add a `// todo` somewhere around there for "death event".