This commit includes the version of the ThreadPool from the official
rust book [1] with a small improvment regarding the pool creation. This
version does not panic if it fails to create the pool it will return a
Result with a possible ThreadPoolCreatError. Everything else is equal to
the tutorial implementation.
[1]
https://doc.rust-lang.org/book/ch20-00-final-project-a-web-server.html