Copied tarsnap role from sovereign
Move tarsnap tasks into main, change names to match standard lowar pattern
Switch backup script to template and move lots of tarsnap config values to variables
Reduce default directories to those we can be sure exist
Add docs for tarsanp role
Comment out postgres related parts of tarsnap script
Make tarsnap machine key into a variable
Keeping the machine key in /root now
Add tarsnap role to module list and cite Alex/Sovereign for it