### What it does
Checks for `fn main() { .. }` in doctests

### Why is this bad?
The test can be shorter (and likely more readable)
if the `fn main()` is left implicit.

### Examples
```
/// An example of a doctest with a `main()` function
///
/// # Examples
///
/// ```
/// fn main() {
///     // this needs not be in an `fn`
/// }
/// ```
fn needless_main() {
    unimplemented!();
}
```