Added alternative redactions syntax for rustfmt

[mitsuhiko]

This adds a new optional redactions syntax for rustfmt support:

#[cfg(feature = "yaml")]
#[test]
fn test_with_random_value_and_trailing_comma_match() {
    assert_yaml_snapshot!(
        &User {
            id: 11,
            username: "john_doe".to_string(),
            email: Email("john@example.com".to_string()),
            extra: "".to_string(),
        },
        match .. {
            ".id" => "[id]",
        }
    );
}

Fixes #419