Events

This is kind of a big diff since events touch pretty much everything. I've implemented every event SDL2 can generate except SysWMEvent. To handle the keycode and scancode listings I use a code generator taken from rust-http. As a part of that I changed the build setup to remove the unneeded configure step. I suspect I'll need to iterate on this for a while but I didn't want to go any further without showing it.

Currently missing are any sort of API outside of enums for the things events dragged in and any API for events beyond polling for them.