Ignore lines that don't begin with cron time fields

[sophieforceno]

I don't know if you're interested in developing this further, but I have a request. I'm not a go programmer, so I can't contribute to it at the moment, unfortunately.

I have some lines in my crontab that don't begin with time fields, for example, variables such as SHELL and MAILTO. c2timer produces an error for these lines, for example:

line "SHELL=/bin/bash" is invalid format

I've worked around this by copying my crontab to a new location and manually removing every line that isn't for a cronjob, but it would be nice to have ct2timer to ignore these lines.

Other than that, great work. This is very useful if you have many cronjobs that you wish to convert to systemd timers.