Added contract::call_with_confirmations().

[akuanti]

Allows you to call a contract function and wait for a specified number of confirmations.

[tomusdrw]

Looks good apart from an unhandled error.

[tomusdrw]

Would be good to handle the error here.

[akuanti]

I'm not sure what is the right way to handle this (still getting used to Rust). Should the function return a Result?

[tomusdrw]

Have a look at:

rust-web3/src/contract/result.rs

Lines 55 to 63 in a9611d3

	impl<T, F, E> From<E> for QueryResult<T, F> where
	E: Into<contract::Error>,
	{
	fn from(e: E) -> Self {
	QueryResult {
	inner: ResultType::Constant(Err(e.into()))
	}
	}
	}

CallResult in that case encapsulate an asynchronous result (positive Ok() and negative Err()).

We should probably have something similar for SendTransactionWithConfirmation type.
It will require introducing new state here:

rust-web3/src/confirm.rs

Line 197 in a9611d3

enum SendTransactionWithConfirmationState<T: Transport> {

that immediately resolves to an error.

[tomusdrw]

Let me know if you need more help with that.

[akuanti]

Yeah, I think I do need more help with this. Are you saying that call_with_confirmations() should still return SendTransactionWithConfirmation, but that SendTransactionWithConfirmation should have an error state so that any errors that happen in the function can be converted into it?

[tomusdrw]

@akuanti I've made a PR to your branch to patch that. Although I'm not super happy with the solution,cause the error types does not match. We can cover that as part of #103 though.