retry-interval a fraction of a second?

[benatkin]

This is quite a powerful tool. Thanks for it! I'm using it to do transfers on s3. While setting up retries I noticed that the --retry-interval is a number of seconds, and checked if fractions of a second are allowed using GitHub search, and found it's restricted to integers. I think either the argument could be made to support decimals (0.2 for 200ms) or an additional mutually exclusive argument for the number of milliseconds before retry could be added. I can make a PR, thought I'd ask how you'd like it designed first though.

[shenwei356]

Thank you, PR is welcome, it would be string (integer+unit), e.g., 1s, 100ms, 1min, even 1min7s