feature request: Let LEDs blink for a certain time

Similar to the vibra.vibrate(millis) function I would like to have a function that lets a LED blink for a certain time without blocking the python part of the card10. I think this is useful as an indicator.

For a start it might be enough to do this for the rockets.

I would like to try the implementation myself as it seems simple enough to mimic the functionality of the vibra.vibrate() function. My suggestion for the interface would be:

leds.blink_rocket(led, value, millis)

Any concerns/opinions/hints about this?!

cheers! zenox