Code review - RW mutex implementation

[helios]

https://github.com/Helios-vmg/rwmutex/tree/master/src

This is a simple multiple-reader, single-writer mutex class for C++14. Reader locks can be upgraded and then downgraded without being released. It uses a queue (allocated on the stack) to prevent writer starvation and to resolve lock acquisition conflicts. Writer lock acquisition requests are always fulfilled in FIFO order.

Thoughts?