A random user-agent

base a project surferua (go-lang) (git@github.com:jiusanzhou/surferua.git) -- thank you

```rs

use crate::randua;

fn main(){ randua::new().firefox().phone().tostring(); // a firefox and mobile user agent randua::new().chrome().phone().tostring(); // a chrome and mobile user agent randua::new().chrome().desktop().tostring(); // a chrome and desktop user agent randua::new().tostring(); // a random user agent }

```