Threadpool Refactor

[COM8]

Refactors cpr::ThreadPool to get rid of all those deadlocks and overly complex code making it at least a bit simpler.

Fixes:

• Thread Pool Deadlock While Task Wait #1040
• Force the end of the thread pool #988

Docs:

• Added cpr::ThreadPool Documentation docs#54

[portsip]

Hi, I would like to suggest use a third thread pool implementation: https://github.com/bshoshany/thread-pool

[COM8]

Hi, I would like to suggest use a third thread pool implementation: https://github.com/bshoshany/thread-pool

Agree. If I'm unable to fix the macos socket issues, I will most likely switch and experiment with that one. Good point.

[portsip]

The ASIO thread pool is also a good choice.

[roemil]

The ASIO thread pool is also a good choice.

Yes! With ASIO threadpool we could get an awaitable Get/Post and use that within a boost coroutine. That would be nice to have.