### What it does
Checks for use of `println`, `print`, `eprintln` or `eprint` in an
implementation of a formatting trait.

### Why is this bad?
Using a print macro is likely unintentional since formatting traits
should write to the `Formatter`, not stdout/stderr.

### Example
```
use std::fmt::{Display, Error, Formatter};

struct S;
impl Display for S {
    fn fmt(&self, f: &mut Formatter) -> Result<(), Error> {
        println!("S");

        Ok(())
    }
}
```
Use instead:
```
use std::fmt::{Display, Error, Formatter};

struct S;
impl Display for S {
    fn fmt(&self, f: &mut Formatter) -> Result<(), Error> {
        writeln!(f, "S");

        Ok(())
    }
}
```