### What it does
Checks `for` loops over slices with an explicit counter
and suggests the use of `.enumerate()`.

### Why is this bad?
Using `.enumerate()` makes the intent more clear,
declutters the code and may be faster in some instances.

### Example
```
let mut i = 0;
for item in &v {
    bar(i, *item);
    i += 1;
}
```

Use instead:
```
for (i, item) in v.iter().enumerate() { bar(i, *item); }
```