Constant async

pub const async: AttributeDescription;

Usage in rsx

let r#async = "value";

rsx! {
    // Attributes need to be under the element they modify
    script {
        // Attributes are followed by a colon and then the value of the attribute
        r#async: "value"
    }
    script {
        // Or you can use the shorthand syntax if you have a variable in scope that has the same name as the attribute
        r#async,
    }
};