Mouse handler refactor

https://github.com/ethmarks/hadronize/commit/3a5adcb

I started working on writing audio code and looking through sound effect libraries, but when I tried to hook my WIP sound-playing function into the mouse handler, I realized what an awful mess my mouse handler code was.

So I spent over an hour refactoring it. While I was at it, I optimized it a tiny bit and fixed the hover thrashing bug that had been bugging me for nearly 2 weeks now.