exponential backoff is too exponential

[bergmark]

I found this counterintuitive:

#[test]
fn backoff() {
    let x: Vec<std::time::Duration> = tokio_retry::strategy::ExponentialBackoff::from_millis(50).take(5).collect();
    dbg!(x);
}

x = [
    50ms,
    2.5s,
    125s,
    6250s,
    312500s,
]

Looking at the source code I would have expected the calculation to be base * factor^retry but it seems that it's base^retry * factor. So to use this like I want it seems that I need to supply from_millis(2).factor(25).

Just swapping this would probably be a confusing breakage, perhaps from_millis could be replaced with from_base? Then it would probably have made me realize that I was doing something wrong.