Consider using `moodycamel::readerwriterqueue` for SpscQueue

[itrofimow]

There exists https://github.com/cameron314/readerwriterqueue, which might be a better fit for concurrent::SpscQueue – it has to be faster than full-featured moodycamel::ConcurrentQueue and it should also require less memory.

There is some confusion between readme and docs: In readme it's stated that

It only supports a two-thread use case (one consuming, and one producing). The threads can't switch roles, ...

However inline docs elaborate that, leaving a room for experimentation.