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

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yoshuawuyts merged 6 commits intoasync-rs:masterfrom

olegnn:option_take_while

Jan 27, 2020

Commits on Jan 12, 2020

Commits on Jan 15, 2020

Commits on Jan 17, 2020

Rewrote `Result`s implementation using `take_while` and `filter_map`
olegnn
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