Implement Serialize trait for Algorithm

[ChrisSchinnerl]

I thought about replacing the SiaEncodable with serde now that we have a serializer.

To avoid a huge PR I thought about doing it piece by piece and this is the first PR updating Algorithm and Address.

[n8maninger]

#[test]
fn test_json_serialize_algorithm() {
	assert_eq!(serde_json::to_string(&Algorithm::ED25519).unwrap(), "\"ed25519\"")
}

#[test]
fn test_json_serialize_address() {
	let address = Address::parse_string("addr:8fb49ccf17dfdcc9526dec6ee8a5cca20ff8247302053d3777410b9b0494ba8cdf32abee86f0").unwrap();
		
	assert_eq!(serde_json::to_string(&address).unwrap(), "\"addr:8fb49ccf17dfdcc9526dec6ee8a5cca20ff8247302053d3777410b9b0494ba8cdf32abee86f0\"")
}