Semaphore support

[Ryzee119]

I have a project that implements both semaphores and mutexes.

Looking very quickly over the code, adding semapore support does not seem too difficult and I am happy to do the work when I get to the point I need them.

Is there any existing work in this area or things that can prevent this from working with the current lib that you are aware of?

[Stevenlawrencehoriba]

I also need this. As it supports locks should not be too bad to add, BUT also need a semaphore wait with a timeout