-h | --help:	prints help message
-d | --debug:	program will print debug messages
-l <file> | --log-to=file:
		prints log messages to file, too. Can be used 0+ times.
<filename>:	last argument is crontab config file,
 			where commands are stored.

all blank and commented lines are ignored
variables look like VAR_NAME = VAR_CONTENT, where previous variables can be used in VAR_CONTENT like:
	VAR1 = a
	VAR2 = $VAR1
	=> VAR1 == a && VAR2 == a.
command lines has 5 time/date fields followed by a command:
	field		allowed value
	-----		-------------
	minute		0-59
	hour		0-23
	day of month	0-30
	month		0-11 (Jan-)
	day of week	0-6 (Sun-)
		^^ allowed value for all fields is asterisk '*',
			which stands for any-value.
	command		command for shell

commands are executed when the minute, hour and month fields match the current time AND when at least one of the two day fields (day of month/week) match.
commands will be run in shell like: `/bin/bash -c 'command'`.
cron examines config every minute.

run:
$ ./mycrontab --log-to=mycrontab.log crontab.conf
$ cat crontab.conf
	LOG = /tmp/crontab.log
	# use /bin/bash to run commands instead of the default /bin/sh
	# run every hour
	0 * * * *	$HOME/bin/daily.job	>> /tmp/jobs
	# run every week at sunday midnight
	0 0 * * 0	$HOME/bin/weekly.job	>> /tmp/jobs
	# run every sunday january and at 1.january at 0:00
	0 0 0 0 0	$HOME/bin/other.job	>> /tmp/jobs