### What it does
Checks for usages of `Mutex<X>` where `X` is an integral
type.

### Why is this bad?
Using a mutex just to make access to a plain integer
sequential is
shooting flies with cannons. `std::sync::atomic::AtomicUsize` is leaner and faster.

### Known problems
This lint cannot detect if the mutex is actually used
for waiting before a critical section.

### Example
```
let x = Mutex::new(0usize);
```

Use instead:
```
let x = AtomicUsize::new(0usize);
```