Add richer error-handling constructs

[aturon]

The trait-based exception handling RFC was postponed for the 1.0 timeframe, but the core team and broader community are generally in favor of this design. We hope to revisit it shortly after the release candidate is produced.

[mitsuhiko]

Is there a chance we could see a fail! macro before 1.0 that does what the error part of the try! macro does at least? The FromError trait is really convenient but currently it feels very much like something like fail! needs to be added.

Eg:

macro_rules! fail {
    ($expr:expr) => (
        return Err(::std::error::FromError::from_error($expr));
    )
}

[arthurprs]

fail! is a nice complement to try! +1 on that

[johanfange]

What about stack traces? Stack traces are immensely useful for diagnosing errors in large long-running applications.

Or is that an orthogonal feature?

[Centril]

We can probably close this now since there are so many various error handling proposals.