thiserror 1.0.10 on Rust Cargo

Improve parsing of .0 and .var-style format arguments (#54)

For example the one here as the argument to the match expression would now be recognized correctly:

#[derive(Error, Debug)]
pub enum MyError {
    #[error("{}: {0}", match .1 {
        Some(n) => format!("a variant error occurred with n={}", n),
        None => format!("there was an empty variant error"),
    })]
    Variant(String, Option<usize>),
}