### What it does
Checks for usage of `option.map(f)` where f is a function
or closure that returns the unit type `()`.

### Why is this bad?
Readability, this can be written more clearly with
an if let statement

### Example
```
let x: Option<String> = do_stuff();
x.map(log_err_msg);
x.map(|msg| log_err_msg(format_msg(msg)));
```

The correct use would be:

```
let x: Option<String> = do_stuff();
if let Some(msg) = x {
    log_err_msg(msg);
}

if let Some(msg) = x {
    log_err_msg(format_msg(msg));
}
```