semaphorus

This crate adds syncronous semaphores to rust.

This is different from like the semaphore crate because

1. semaphorus supports #![no_std]
2. semaphorus doesn't use Arc under the hood and behaves more like RwLock<T>, this does require the semaphores to be in an Arc for multithreading as they don't implement clone

lib.rs:

semaphorus add a Semaphore type that behaves like a RwLock