### What it does
This lint warns about the use of literals as `print!`/`println!` args.

### Why is this bad?
Using literals as `println!` args is inefficient
(c.f., https://github.com/matthiaskrgr/rust-str-bench) and unnecessary
(i.e., just put the literal in the format string)

### Known problems
Will also warn with macro calls as arguments that expand to literals
-- e.g., `println!("{}", env!("FOO"))`.

### Example
```
println!("{}", "foo");
```
use the literal without formatting:
```
println!("foo");
```