multiprocessing.pool.Pool.map should take more than one iterable

[ycm.jason at gmail.com]

Hello all,

The official doc describes `Pool.map(func, iterable[, chunksize])` as "A parallel equivalent of the map() built-in function.". 

Since the function signature of `map` is `map(function, iterable, ...)`, I hereby suggest that `Pool.map` should change its function signature to `Pool.map(function, iterable, ... [, chunksize])`. This will bring true equivalent to these functions.

Tell me what you think. 

Pool.map: https://docs.python.org/3/library/multiprocessing.html#multiprocessing.pool.Pool.map

map: https://docs.python.org/3/library/functions.html#map

Jason