Use `take_while` instead of `scan` in `impl` of `Product`, `Sum` and `FromStream` for `Option` and `Result`#667

yoshuawuyts merged 6 commits intoasync-rs:masterasync-rs/async-std:masterfrom

olegnn:option_take_whileolegnn/async-std:option_take_whileCopy head branch name to clipboard