Stronger typing on `crate::helper::Node` type

[ralexstokes]

my_kademlia/src/helper.rs

Lines 13 to 14 in 9bd1cff

	pub ip_address: &'static str,
	pub udp_port: &'static str,

there are conventional types for these data, e.g. something like (https://doc.rust-lang.org/std/net/struct.Ipv4Addr.html, u16)

[ralexstokes]

fixed in #7