Add a Macro Benchmark that Exercises Threading (Multi-Core Concurrency)

From @methane (https://mail.python.org/archives/list/python-dev@python.org/message/KVH7QLJ4VJBQQ45LZTWDXO2SEC6ANX7T/):

CPU cache invalidation exists regardless. With the current GIL the
effect it is reduced significantly.

It's an interesting point. We can not see the benefit from pypeformance, because it doesn't use much data and it runs one process
at a time. So the pyperformance can not make enough stress to the last level cache which is shared by many cores.

We need multiprocess performance benchmark apart from pyperformance, to stress the last level cache from multiple cores. It helps not only this PEP, but also optimizing containers like dict and set.

既存の pyperformance ベンチマークスイートと、単一プロセスベンチマークがどのように構成されているかを確認することから始めます。multiprocessing ベンチマークがコア間で共有されるラストレベルキャッシュにどのような負荷をかけるべきかを定義し、dict と set の最適化の評価に役立つ再現可能なマルチコア性能データを提供できた時点でベンチマークが完成したと見なします。