Accept top level #[error(...)] attribute on enums to apply to all variants

[dtolnay]

use thiserror::Error;

#[derive(Error, Debug)]
#[error("{0}")]
pub enum Error {
    Io(io::Error),
    Json(serde_json::Error),
    Regex(regex::Error),
}

^ this should be treated as equivalent to:

#[derive(Error, Debug)]
pub enum Error {
    #[error("{0}")]
    Io(io::Error),
    #[error("{0}")]
    Json(serde_json::Error),
    #[error("{0}")]
    Regex(regex::Error),
}

[MOZGIII]

This works, but what if I want to customize one of the variants?