Add synchronization primitives

[planetis-m]

Examples are kept in a separate folder, although Im thinking of making them later runnableExamples. All but the spinlock depend on std/locks

[planetis-m]

Nim 1.4 lacks broadcast so thats why the barrier test fail.

[Araq]

Nim 1.4 lacks broadcast so thats why the barrier test fail.

So add a version check for these tests or better yet a when declared(broadcast)

[planetis-m]

Is porting C++ primitives https://github.com/llvm/llvm-project/blob/main/libcxx/include/semaphore doable? I think the lock based semaphore is overly restrictive, however I am not even sure that code can be ported over different compilers/OSes.

[Araq]

I only skimmed the C++ code but it looks doable.

[planetis-m]

My issue is atomic.wait_all which is platform depended. Implemented with futexes under linux. If someone figures the hard part, then the rest are easy.

[planetis-m]

@Araq this is ready for merge. shout still no broadcasting support in the CI

[konsumlamm]

What is the status of this? I know that there is https://github.com/planetis-m/sync, but I think it would still be useful to have some more synchronization primitives here. latch is superseded by waitgroups afaict. I'm not so sure about spinlock, since usually you want to use normal locks instead. The others are pretty common synchronization primitives though.

[Araq]

Please split up this PR.

[planetis-m]

Sorry I don't have any available time to modernize and split this PR.

[planetis-m]

superseeded by #47