Resume Hook (Hibernation)

[loadfred]

• Added resume hook
• Also added resume to docs and readme
• Not for swap files, only for swap partitions

Uses resolve_device for the resume variable in config. Then uses printf and stat to get major:minor numbers of the partition and puts that into /sys/power/resume.
Works with my luks/lvm kiss linux with swap partition under luks/lvm (resumes after luks password is entered). Should work for any other swap setup (except swap files).

[illiliti]

I would do copy_exec printf too since printf can be implemented as a command and not available as shell builtin. Also I afraid we can't afford to use stat. Its interface is not portable because not all implementations have compatible flags. Therefore we need a different way to derive major:minor numbers from a devnode and luckily there is such way: read -r dev < /sys/class/block/<basename of devnode>/dev. With it you don't even need printf, but to be honest I'm not sure if it's usable at all. Would you mind to test if it works for you?

[loadfred]

To get the basename I got the original device with readlink. And instead of using read to put the major:minor into another variable, I just used cat to place it in /sys/power/resume. Also, instead of having the readlink in a separate variable I could have used: cat /sys/class/block/$(basename $(readlink "$device"))/dev > /sys/power/resume.
Both methods work with no errors, I just didn't use basename because it was one more program to copy_exec.
It might be able to be simplier, I'm not sure.