Allow the Transport to have a different kind of information for the target ChoreographyLocation

[ihaveint]

This allows the user to specify different types of information for the target location when building the transport.

if users want to make a HttpTransport, they currently do this:

use crate::transport::TransportConfig;
use crate::transport_config;

// for http transport:
let config = transport_config!(
                Alice => ("0.0.0.0".to_string(), 9021),
                Bob: ("localhost".to_string(), 9020)
                Carol: ("localhost".to_string(), 9022)
            );
let alice_transport = HttpTransport::new(&config);

But with this pull request, we support custom Transports where the information type for Alice is different then the one for Bob and Carol. Something like this:

// for a custom transport:
let config = transport_config!(
                Alice => value_of_type_a,
                Bob: value_of_type_b,
                Carol: another_value_of_type_b
            );

let alice_transport = CustomTransport::new(&config);