Add mapParallel and forEachParallel

[tracker1]

Would be nice to see a forEach that allowed for parallel execution..

• mapParallel(array, options, callback, [thisArg])
• forEachParallel(array, options, callback, [thisArg])

options

• concurrency: number, min: 1, max: ????
  • The number of in-flight/unresolved concurrent operations to start.

[toniov]

map and forEach are already run concurrently.

Certainly a concurrency parameter would be nice, but I want to keep the main methods with the same API as the original ES5 ones.

Adding forEachLimit, mapLimit, etc. could be the way to go. Similar to the async library xxxLimit methods.