Support tx parameter overrides

[digorithm]

This PR adds support for setting parameters to contract calls and deployments. These parameters are byte price, gas limit, and gas price for now.

It's done through a new method tx_params() that's chained to the generated ABI method:

let result = contract_instance
        .initialize_counter(42) // Build the ABI call
        .tx_params(Parameters::new(None, Some(1_000_000), None)) // <--- this here.
        .call() // Perform the network call
        .await
        .unwrap();

This doesn't break the way contract calls were made previously. i.e. initialize_counter(42).call(); (without .tx_params()) works just like before and, also just like before, it will use default values for these parameters. If the user wants to override the default values, then they can chain tx_params() to the method call.

However, this does break previous contract deployments, as the deployment method now requires these params to be set:

 let contract_id =
        Contract::deploy(&compiled, &provider, &wallet, Parameters::default())
            .await
            .unwrap();

Closes #138.

[adlerjohn]

I'm not the biggest fan of the name with_params and Parameters. My initial reaction to .call().with_params() is that those are parameters for the call, not the transaction. Maybe .tx_params() and TxParameters?

[digorithm]

I'm not the biggest fan of the name with_params and Parameters. My initial reaction to .call().with_params() is that those are parameters for the call, not the transaction. Maybe .tx_params() and TxParameters?

Yeah, I wasn't attached to the with_params/params naming. Will update it soon.

[adlerjohn]

LGTM, but will defer to @vnepveu

[iqdecay]

Some naming issues, 1/2 nits and 1/2 questions to make sure I understand. Otherwise great!!!