Steam OpenID

This is a simple implementation of OpenID for Steam authorization used by Velocity Vault.

How to

```Rust let openid = SteamOpenId::new("http://localhost:8080", "/callback").unwrap();

// Redirect the user to this url: let redirecturl = openid.getredirect_url();

// Then in your callback: let steamid64 = openid.verify(req.query_string()).unwrap(); ```