Udev input driver for Linux

This adds udev input driver for keyboard and mouse.
This allows mouse to work outside X. It also supports hotplugging, and can support multiple keyboard/mice with epoll.
Like udev joypads, it requires libudev for device discovery and hotplugging.

When tested properly, it can replace linuxraw. It doesn't hijack stdin with tty hacks.
You might need to set permissions for /dev/input/event* devices. On Arch, they seem to be root-only by default.

Missing: keyboard callback