make ConfigUtil not OO
print stack trace when FATAL
can't call GET before parse config end
	modified:   README.md
	modified:   STEP/CommonUtil.pm
	modified:   STEP/ConfigUtil.pm
	modified:   STEP/Helper.pm
	modified:   default_farm.pm
	modified:   demo_config.pm
	modified:   slave.pl
	modified:   step