[feature] Add more functions

[jan-janssen]

The multiprocessing Pool implements more functions than just the map() function: https://docs.python.org/3/library/multiprocessing.html#module-multiprocessing.pool

• apply()
• apply_async()
• map()
• map_async()
• imap()
• imap_unordered()
• starmap()
• starmap_async()

[jan-janssen]

The Pool class was replaced by the Executor class.