Issue #10: Random delay

What do you think, if Delay would be an array?

If there is 1 number in the array, the delay will be equal to this number.
If there are two numbers in the array, the delay would get random number in between.
This requires us to always pass an array as the delay, even if it’s set to a fixed number. It’d be better if it accepts *either* a number or an array. In the latter case, it uses the first and second element as the lower and upper boundaries for the random delay. So the conditional here would work as a type check for `number` and `array`.

But again, please make these changes in the CoffeeScript and just check in the compiled JS version.