Would you consider providing macros?

[NickLarsenNZ]

I have used a Python decorator in the past, and wondered if you might consider providing a proc_macro to reduce boiler plate. I'm quit new to proc_macro, but I could give it a try.

examples/retry.rs could become:

#[retry(ExponentialBackoff)]
fn fetch_url(url: &str) -> Result<String, Error<reqwest::Error>> {
    println!("Fetching {}", url);
    let mut resp = reqwest::blocking::get(url)?;

    let mut content = String::new();
    let _ = resp.read_to_string(&mut content);
    Ok(content)
}