Get the difference between two times in second

Property definitions

date $ Time :: diff_time
	# Get the difference between two times in second
	fun diff_time(other: Time): Int do
		return (hour * 3600 + minute * 60 + second) -
			(other.hour * 3600 + other.minute * 60 + other.second)
	end
lib/date/date.nit:64,2--68,4