Adds input event interface AKA evdev found on most modern Linuxes.
Mostly feature-complete, missing parts are:
- power and force-feedback events support
- "euclidean bipartite matching" problem solver
- man pages
This patch is kernel API only, evdev support for some individual drivers can be found here: https://github.com/wulf7/freebsd/tree/evdev
Heavily based on GSOC2014 project by Jakub Klama