generator: suggestiosn from wavexx
try to keep user crontabs secret, as expected
reference /var/lib/systemd/timers in manpage
rework generator manpage for consistency with systemd builtin generators
forcefully restart all units on file updates
inhibit /etc/cron.boot/ after first execution (issue #30)
issue #30: update readme
don't run mail_on_failure as root
Calculate a stable ID for persistent jobs