async: Corrected APIs from forEach* to each*

The following APIs are incorrect and do not exist:
forEach
forEachSeries
forEachLimit

This commit refactors them to the following respectively:
each (https://github.com/caolan/async#each)
eachSeries (https://github.com/caolan/async#eachSeries)
eachLimit (https://github.com/caolan/async#eachLimit)

Additionally it adds a test for forEachSeries, which was missing.