Contract calls and abigen integration

[digorithm]

This PR introduces the integration of contract calls and the previous abigen! functionality.

Meaning that, now, the Rust bindings generated from the JSON ABI can build a script and script_data on the fly and call an ABI method from a deployed contract.

This is part of a larger work documented at FuelLabs/sway#124.

Example:

let salt: [u8; 32] = rng.gen();
let salt = Salt::from(salt);

let compiled =
    Contract::compile_sway_contract("tests/test_projects/contract_test", salt).unwrap();

let (client, contract_id) = Contract::launch_and_deploy(&compiled).await.unwrap();

println!("Contract deployed @ {:x}", contract_id);

let contract_instance = MyContract::new(compiled, client);

let result = contract_instance
    .initialize_counter(42) // Build the ABI call
    .call() // Perform the network call
    .await
    .unwrap();

assert_eq!(42, result.unwrap());

let result = contract_instance
    .increment_counter(10)
    .call()
    .await
    .unwrap();

assert_eq!(52, result.unwrap());

[AlicanC]

I removed gas/coin/color from the ABI JSON and hardcoded them in our function selector generator for this. Your solution looks better but we are going to remove these anyways so I'm going to keep my dirty solution 😄

[digorithm]

Hahaha, yeah, seems like we both had to come up with dirty solutions for this. It bothers me a little bit, but this (and your approach too) is the simplest one to "revert" once these are removed from the ABI JSON.

[adlerjohn]

Can you guys file issues to go back and remove the hack once the Sway compiler fixes this?

[digorithm]

Done #13 and FuelLabs/fuels-ts#71

[adlerjohn]