Logic moved from truckle to cave.

truckle commands to cave added: `cave do`, `cave retry`, `cave upgrade`
You do not need truckle upgrade, now sudo cave upgrade works, too.
These commands do not depend on truckle, it works fine with cave-only.

Environment variables added via `/etc/profile.d/cave.sh`.
At the moment only resume-file-depended variables
(TRUCKLE_RESUME_FILE, CAVE_RESUME_OPTIONS, CAVE_RESOLVE_OPTIONS, ...)
If you use cave, the resume-file will be used automaticaly.
You do not need truckle anymore to have auto-resume-files.
But sudo will remove these from env...

Sudoers-config for cave added via `/etc/sudoers.d/cave`.
sudo will keep the same variables like defined in `/etc/profile.d/cave.sh`.
I do not know, but i think it can be a security hole.
But never allow users to use cave as root!
So, now you can use sudo, too.

These combinations of new cave-related changes will allow this:

  sudo cave upgrade
  sudo cave do
  # something went wrong?
  sudo cave retry

Only pagered it is easier with truckle:

  sudo cave -cy upgrade | less -R
  # vs.
  truckle upgrade