(#145) - optional map callback

It is a follow up of #252 where you can find an attempt to fix issue #145 to make map callback optional. However it looks like tests attached to #252 are broken.

As we can't use callback here I added timeouts which follow the convension of 25ms break between events. And so map and mapLimit got 100ms (since mapIterator generates 75ms for argument 3) and mapSeries got 175ms ((1+3+2) * 25ms + 25ms).