[Python-Dev] API and process questions (sparked by Claudiu Popa on 16104

[Claudiu Popa]

This issue raised too much bikeshedding. To wrap it up, I'll modify
the patch with the following:

- processes renamed to workers
- `workers` defaults to 1
- When `workers` is equal to 0, then `os.cpu_count` will be used
- When `workers` > 1, multiple processes will be used
- When `workers` == 1, run normally (no multiple processes)
- Negative values really should raise a ValueError (as
multiprocessing.Pool and soon
  concurrent.futures.Thread/ProcessPoolExecutor)
- Will raise NotImplementedError if multiprocessing can't be used
(when `workers` equals to 0 or > 1)

If anyone agrees with the above, then I'll modify the patch. This will
be its last iteration, any other bikeshedding
should be addressed by the core dev who'll apply it.

Thank you.