close issue #29: support new timer schedule in systemd 217
fix new lintian warning: manpage-has-errors-from-man usr/share/man/man7/systemd.cron.7.gz 124: warning [p 3, 3.0i]: cannot adjust line
generator: don't waste time parsing empty lines
generator: check for argv[1]
let user disable Persistent=true heuristic with dummy PERSISTENT= variable