Multi commands

As we are managing *multiple* cronjobs in a large application, it's more manageable to create one cronjob file with multiple times/commands instead of one cron file per time/command.

This code is a rough draft: it could be tweaked to set default values for empty hash parameters (minutes, hours, etc) and some ideas you might have! 

So if this feature is useful to you, I could spend more time improving it. 

Have fun!