ruby timestamp milliseconds
http://stackoverflow.com/questions/20001883/ruby-convert-datetime-to-milliseconds
require 'date' p DateTime.now.strftime('%s') # "1384526946" (seconds) p DateTime.now.strftime('%Q') # "1384526946523" (milliseconds) 무엇이 좋을까?
>> (Time.now.to_f * 1000).to_s "1421401335422.171"
>> DateTime.now.strftime('%Q') "1421401350926"
















