Add an ex/ directory showing how to enable powersave as boot

This is done via modules options, udev rules and sysctl config.
These files are mostly stolen from
https://github.com/Unia/Powersave (branch edge)
and also from
https://github.com/vodik/powersave/ and https://github.com/intelfx/power-management
Put udev rules in rules.d
Rework README and add COPYING