Implement the Default Trait Along with new()

Sources:
https://rust-lang.github.io/rust-clippy/master/#new_without_default
https://rust-unofficial.github.io/patterns/idioms/default.html

The user of your type might expect to be able to use Default. It is also more convenient for you.

#![allow(unused)]
fn main() {
struct Ex {
    field1: i32,
    field2: i32,
}

impl Ex {
    fn new() -> Self {
        Ex {
            field1: 0,
            field2: 0,
        }
    }
}

impl std::default::Default for Ex {
    fn default() -> Self {
        Ex::new()
    }
}
}