I2P domains

as understand, domain zone rule excludes digits - `.onion` works, but `.i2p` does not.
also `ws://xxx.b32.i2p` works but `http://xxx.b32.i2p` - does not.

``` src/domains.rs
fn valid_tld(tld: &str) -> bool {
    tld.chars()
        .take_while(|c| c.is_ascii_alphabetic())
        .take(2)
        .count()
        >= 2
}
```