Init Argument

[TheWisker]

I changed the behavior a little by making rubato.timed only execute the subscribed function on object creation (initially) when the init argument is passed to it. In my case this was necessary as some objects used in the subscribed function where only defined just before setting rubato.timed.target thus when the subscribed function was executed prematurely an error was thrown as those objects were always nil at that time. Thanks for this awesome library!