Make it possible to change "now"

[J00nz]

As a developer it would be very nice to have a way to override the internal "now" functionality.

I realize that it is possible to send it, or rather "time2, as a argument when invoking methods, but that is a very cumbersome way of doing it.

I propose a way to simply "setNow" that takes a function as a argument and overrides "now" to this.

It would make implementations that modifies the "rate" of time much more convenient to do.

[linorabolini]

This is golden. Any clues on when it would be published ?